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 $59.37   13.844%   $67.5892   $67.59   $67.60   $67.60  
  Purchase #2 $89.98   13.735%   $102.3388   $102.34   $102.35   $102.30  
  Purchase #3 $177.86   13.131%   $201.2148   $201.21   $201.20   $201.20  
  Purchase #4 $46.50   5.298%   $48.9636   $48.96   $48.95   $49.00  
  Purchase #5 $151.96   10.517%   $167.9416   $167.94   $167.95   $167.90  
  Purchase #6 $91.91   11.323%   $102.317   $102.32   $102.30   $102.30  
  Purchase #7 $213.46   8.343%   $231.269   $231.27   $231.25   $231.30  
  7 purchase totals = $831.04       $921.6340   $921.63   $921.60   $921.60