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 $84.35   13.708%   $95.9127   $95.91   $95.90   $95.90  
  Purchase #2 $234.55   11.669%   $261.9196   $261.92   $261.90   $261.90  
  Purchase #3 $229.42   13.759%   $260.9859   $260.99   $261.00   $261.00  
  Purchase #4 $221.52   12.408%   $249.0062   $249.01   $249.00   $249.00  
  Purchase #5 $244.95   9.220%   $267.5344   $267.53   $267.55   $267.50  
  Purchase #6 $80.93   8.736%   $88   $88.00   $88.00   $88.00  
  Purchase #7 $170.82   5.623%   $180.4252   $180.43   $180.45   $180.40  
  7 purchase totals = $1,266.54       $1,403.7840   $1,403.79   $1,403.80   $1,403.70