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 $68.81   11.819%   $76.9427   $76.94   $76.95   $76.90  
  Purchase #2 $8.72   7.636%   $9.3859   $9.39   $9.40   $9.40  
  Purchase #3 $218.30   6.353%   $232.1686   $232.17   $232.15   $232.20  
  Purchase #4 $162.69   8.485%   $176.4942   $176.49   $176.50   $176.50  
  Purchase #5 $170.76   11.221%   $189.921   $189.92   $189.90   $189.90  
  Purchase #6 $168.45   5.650%   $177.9674   $177.97   $177.95   $178.00  
  Purchase #7 $244.55   6.731%   $261.0107   $261.01   $261.00   $261.00  
  7 purchase totals = $1,042.28       $1,123.8905   $1,123.89   $1,123.85   $1,123.90