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 $51.92   10.697%   $57.4739   $57.47   $57.45   $57.50  
  Purchase #2 $97.50   13.253%   $110.4217   $110.42   $110.40   $110.40  
  Purchase #3 $220.57   6.736%   $235.4276   $235.43   $235.45   $235.40  
  Purchase #4 $96.93   7.871%   $104.5594   $104.56   $104.55   $104.60  
  Purchase #5 $113.38   5.669%   $119.8075   $119.81   $119.80   $119.80  
  Purchase #6 $184.73   10.637%   $204.3797   $204.38   $204.40   $204.40  
  Purchase #7 $167.48   13.684%   $190.398   $190.40   $190.40   $190.40  
  7 purchase totals = $932.51       $1,022.4678   $1,022.47   $1,022.45   $1,022.50