Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $234.31   5.869%   $248.0617   $248.06   $248.05   $248.10  
  Purchase #2 $127.79   12.443%   $143.6909   $143.69   $143.70   $143.70  
  Purchase #3 $152.33   7.654%   $163.9893   $163.99   $164.00   $164.00  
  Purchase #4 $133.52   13.305%   $151.2848   $151.28   $151.30   $151.30  
  Purchase #5 $59.89   11.665%   $66.8762   $66.88   $66.90   $66.90  
  Purchase #6 $227.73   8.114%   $246.208   $246.21   $246.20   $246.20  
  Purchase #7 $151.75   3.472%   $157.0188   $157.02   $157.00   $157.00  
  7 purchase totals = $1,087.32       $1,177.1297   $1,177.13   $1,177.15   $1,177.20