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 $58.77   13.176%   $66.5135   $66.51   $66.50   $66.50  
  Purchase #2 $100.54   3.587%   $104.1464   $104.15   $104.15   $104.10  
  Purchase #3 $228.80   3.133%   $235.9683   $235.97   $235.95   $236.00  
  Purchase #4 $77.65   9.291%   $84.8645   $84.86   $84.85   $84.90  
  Purchase #5 $207.57   12.111%   $232.7088   $232.71   $232.70   $232.70  
  Purchase #6 $109.88   12.288%   $123.3821   $123.38   $123.40   $123.40  
  Purchase #7 $88.76   6.733%   $94.7362   $94.74   $94.75   $94.70  
  7 purchase totals = $871.97       $942.3198   $942.32   $942.30   $942.30