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 $247.99   6.650%   $264.4813   $264.48   $264.50   $264.50  
  Purchase #2 $151.92   3.768%   $157.6443   $157.64   $157.65   $157.60  
  Purchase #3 $5.49   6.518%   $5.8478   $5.85   $5.85   $5.80  
  Purchase #4 $61.44   11.103%   $68.2617   $68.26   $68.25   $68.30  
  Purchase #5 $173.49   5.301%   $182.6867   $182.69   $182.70   $182.70  
  Purchase #6 $65.29   6.619%   $69.6115   $69.61   $69.60   $69.60  
  Purchase #7 $172.82   13.353%   $195.8967   $195.90   $195.90   $195.90  
  7 purchase totals = $878.44       $944.4300   $944.43   $944.45   $944.40