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 $206.27   5.208%   $217.0125   $217.01   $217.00   $217.00  
  Purchase #2 $156.69   8.472%   $169.9648   $169.96   $169.95   $170.00  
  Purchase #3 $211.86   13.665%   $240.8107   $240.81   $240.80   $240.80  
  Purchase #4 $118.96   5.689%   $125.7276   $125.73   $125.75   $125.70  
  Purchase #5 $46.52   4.821%   $48.7627   $48.76   $48.75   $48.80  
  Purchase #6 $231.41   3.118%   $238.6254   $238.63   $238.65   $238.60  
  Purchase #7 $187.27   11.634%   $209.057   $209.06   $209.05   $209.10  
  7 purchase totals = $1,158.98       $1,249.9607   $1,249.96   $1,249.95   $1,250.00