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 $221.54   10.323%   $244.4096   $244.41   $244.40   $244.40  
  Purchase #2 $40.84   13.373%   $46.3015   $46.30   $46.30   $46.30  
  Purchase #3 $179.53   7.843%   $193.6105   $193.61   $193.60   $193.60  
  Purchase #4 $246.87   5.733%   $261.0231   $261.02   $261.00   $261.00  
  Purchase #5 $148.81   8.490%   $161.444   $161.44   $161.45   $161.40  
  Purchase #6 $98.50   12.219%   $110.5357   $110.54   $110.55   $110.50  
  Purchase #7 $46.30   9.800%   $50.8374   $50.84   $50.85   $50.80  
  7 purchase totals = $982.39       $1,068.1618   $1,068.16   $1,068.15   $1,068.00