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 $221.75   13.428%   $251.5266   $251.53   $251.55   $251.50  
  Purchase #2 $217.39   8.485%   $235.8355   $235.84   $235.85   $235.80  
  Purchase #3 $173.31   8.713%   $188.4105   $188.41   $188.40   $188.40  
  Purchase #4 $77.62   9.733%   $85.1748   $85.17   $85.15   $85.20  
  Purchase #5 $132.77   12.531%   $149.4074   $149.41   $149.40   $149.40  
  Purchase #6 $56.87   12.576%   $64.022   $64.02   $64.00   $64.00  
  Purchase #7 $64.55   9.195%   $70.4854   $70.49   $70.50   $70.50  
  7 purchase totals = $944.26       $1,044.8622   $1,044.87   $1,044.85   $1,044.80