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 $144.81   3.277%   $149.5554   $149.56   $149.55   $149.60  
  Purchase #2 $49.51   10.596%   $54.7561   $54.76   $54.75   $54.80  
  Purchase #3 $11.69   12.601%   $13.1631   $13.16   $13.15   $13.20  
  Purchase #4 $229.85   8.295%   $248.9161   $248.92   $248.90   $248.90  
  Purchase #5 $104.60   13.794%   $119.0285   $119.03   $119.05   $119.00  
  Purchase #6 $173.65   5.203%   $182.685   $182.69   $182.70   $182.70  
  Purchase #7 $235.87   12.530%   $265.4245   $265.42   $265.40   $265.40  
  7 purchase totals = $949.98       $1,033.5287   $1,033.54   $1,033.50   $1,033.60