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 $125.25   13.361%   $141.9847   $141.98   $142.00   $142.00  
  Purchase #2 $54.49   13.290%   $61.7317   $61.73   $61.75   $61.70  
  Purchase #3 $214.77   11.594%   $239.6704   $239.67   $239.65   $239.70  
  Purchase #4 $177.95   7.874%   $191.9618   $191.96   $191.95   $192.00  
  Purchase #5 $101.30   6.821%   $108.2097   $108.21   $108.20   $108.20  
  Purchase #6 $17.58   8.862%   $19.1379   $19.14   $19.15   $19.10  
  Purchase #7 $64.62   5.675%   $68.2872   $68.29   $68.30   $68.30  
  7 purchase totals = $755.96       $830.9834   $830.98   $831.00   $831.00