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 $242.76   13.517%   $275.5739   $275.57   $275.55   $275.60  
  Purchase #2 $193.93   6.397%   $206.3357   $206.34   $206.35   $206.30  
  Purchase #3 $200.92   5.383%   $211.7355   $211.74   $211.75   $211.70  
  Purchase #4 $244.26   12.427%   $274.6142   $274.61   $274.60   $274.60  
  Purchase #5 $97.74   12.593%   $110.0484   $110.05   $110.05   $110.00  
  Purchase #6 $238.66   12.653%   $268.8576   $268.86   $268.85   $268.90  
  Purchase #7 $221.65   9.312%   $242.29   $242.29   $242.30   $242.30  
  7 purchase totals = $1,439.92       $1,589.4553   $1,589.46   $1,589.45   $1,589.40