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 $208.78   10.329%   $230.3449   $230.34   $230.35   $230.30  
  Purchase #2 $24.76   5.466%   $26.1134   $26.11   $26.10   $26.10  
  Purchase #3 $234.38   11.243%   $260.7313   $260.73   $260.75   $260.70  
  Purchase #4 $245.54   12.479%   $276.1809   $276.18   $276.20   $276.20  
  Purchase #5 $238.50   9.284%   $260.6423   $260.64   $260.65   $260.60  
  Purchase #6 $114.81   4.758%   $120.2727   $120.27   $120.25   $120.30  
  Purchase #7 $232.80   5.216%   $244.9428   $244.94   $244.95   $244.90  
  7 purchase totals = $1,299.57       $1,419.2283   $1,419.21   $1,419.25   $1,419.10