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 $95.38   11.372%   $106.2266   $106.23   $106.25   $106.20  
  Purchase #2 $59.34   12.471%   $66.7403   $66.74   $66.75   $66.70  
  Purchase #3 $58.29   3.663%   $60.4252   $60.43   $60.45   $60.40  
  Purchase #4 $250.36   13.241%   $283.5102   $283.51   $283.50   $283.50  
  Purchase #5 $116.26   7.843%   $125.3783   $125.38   $125.40   $125.40  
  Purchase #6 $226.29   13.433%   $256.6875   $256.69   $256.70   $256.70  
  Purchase #7 $177.65   12.360%   $199.6075   $199.61   $199.60   $199.60  
  7 purchase totals = $983.57       $1,098.5756   $1,098.59   $1,098.65   $1,098.50