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 $148.68   9.146%   $162.2783   $162.28   $162.30   $162.30  
  Purchase #2 $48.85   10.464%   $53.9617   $53.96   $53.95   $54.00  
  Purchase #3 $11.76   10.505%   $12.9954   $13.00   $13.00   $13.00  
  Purchase #4 $61.40   9.140%   $67.012   $67.01   $67.00   $67.00  
  Purchase #5 $94.79   8.493%   $102.8405   $102.84   $102.85   $102.80  
  Purchase #6 $208.47   10.316%   $229.9758   $229.98   $230.00   $230.00  
  Purchase #7 $179.85   12.432%   $202.209   $202.21   $202.20   $202.20  
  7 purchase totals = $753.80       $831.2727   $831.28   $831.30   $831.30