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 $132.43   10.253%   $146.008   $146.01   $146.00   $146.00  
  Purchase #2 $110.92   7.746%   $119.5119   $119.51   $119.50   $119.50  
  Purchase #3 $197.73   4.198%   $206.0307   $206.03   $206.05   $206.00  
  Purchase #4 $97.53   11.756%   $108.9956   $109.00   $109.00   $109.00  
  Purchase #5 $107.93   12.156%   $121.05   $121.05   $121.05   $121.10  
  Purchase #6 $51.55   4.541%   $53.8909   $53.89   $53.90   $53.90  
  Purchase #7 $183.95   10.731%   $203.6897   $203.69   $203.70   $203.70  
  7 purchase totals = $882.04       $959.1768   $959.18   $959.20   $959.20