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 $236.67   8.445%   $256.6568   $256.66   $256.65   $256.70  
  Purchase #2 $228.71   6.622%   $243.8552   $243.86   $243.85   $243.90  
  Purchase #3 $69.66   12.209%   $78.1648   $78.16   $78.15   $78.20  
  Purchase #4 $152.91   9.483%   $167.4105   $167.41   $167.40   $167.40  
  Purchase #5 $81.69   11.768%   $91.3033   $91.30   $91.30   $91.30  
  Purchase #6 $146.67   8.467%   $159.0885   $159.09   $159.10   $159.10  
  Purchase #7 $243.95   9.519%   $267.1716   $267.17   $267.15   $267.20  
  7 purchase totals = $1,160.26       $1,263.6507   $1,263.65   $1,263.60   $1,263.80