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 $44.56   12.246%   $50.0168   $50.02   $50.00   $50.00  
  Purchase #2 $173.92   6.429%   $185.1013   $185.10   $185.10   $185.10  
  Purchase #3 $163.69   11.612%   $182.6977   $182.70   $182.70   $182.70  
  Purchase #4 $66.34   11.854%   $74.2039   $74.20   $74.20   $74.20  
  Purchase #5 $200.73   7.180%   $215.1424   $215.14   $215.15   $215.10  
  Purchase #6 $98.38   5.677%   $103.965   $103.97   $103.95   $104.00  
  Purchase #7 $122.55   6.519%   $130.539   $130.54   $130.55   $130.50  
  7 purchase totals = $870.17       $941.6661   $941.67   $941.65   $941.60