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 $53.32   11.774%   $59.5979   $59.60   $59.60   $59.60  
  Purchase #2 $58.65   6.382%   $62.393   $62.39   $62.40   $62.40  
  Purchase #3 $81.45   4.141%   $84.8228   $84.82   $84.80   $84.80  
  Purchase #4 $117.83   3.317%   $121.7384   $121.74   $121.75   $121.70  
  Purchase #5 $222.89   9.751%   $244.624   $244.62   $244.60   $244.60  
  Purchase #6 $189.32   12.468%   $212.9244   $212.92   $212.90   $212.90  
  Purchase #7 $6.66   9.463%   $7.2902   $7.29   $7.30   $7.30  
  7 purchase totals = $730.12       $793.3907   $793.38   $793.35   $793.30