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 $59.43   4.303%   $61.9873   $61.99   $62.00   $62.00  
  Purchase #2 $92.68   8.459%   $100.5198   $100.52   $100.50   $100.50  
  Purchase #3 $45.55   10.411%   $50.2922   $50.29   $50.30   $50.30  
  Purchase #4 $236.36   10.590%   $261.3905   $261.39   $261.40   $261.40  
  Purchase #5 $229.66   13.222%   $260.0256   $260.03   $260.05   $260.00  
  Purchase #6 $194.88   7.117%   $208.7496   $208.75   $208.75   $208.70  
  Purchase #7 $99.45   9.182%   $108.5815   $108.58   $108.60   $108.60  
  7 purchase totals = $958.01       $1,051.5465   $1,051.55   $1,051.60   $1,051.50