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 $227.65   8.742%   $247.5512   $247.55   $247.55   $247.60  
  Purchase #2 $243.92   13.485%   $276.8126   $276.81   $276.80   $276.80  
  Purchase #3 $201.49   11.640%   $224.9434   $224.94   $224.95   $224.90  
  Purchase #4 $204.38   11.240%   $227.3523   $227.35   $227.35   $227.40  
  Purchase #5 $237.36   13.300%   $268.9289   $268.93   $268.95   $268.90  
  Purchase #6 $236.62   7.435%   $254.2127   $254.21   $254.20   $254.20  
  Purchase #7 $200.94   10.214%   $221.464   $221.46   $221.45   $221.50  
  7 purchase totals = $1,552.36       $1,721.2651   $1,721.25   $1,721.25   $1,721.30