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 $209.71   6.827%   $224.0269   $224.03   $224.05   $224.00  
  Purchase #2 $184.72   11.201%   $205.4105   $205.41   $205.40   $205.40  
  Purchase #3 $54.95   13.207%   $62.2072   $62.21   $62.20   $62.20  
  Purchase #4 $114.91   3.157%   $118.5377   $118.54   $118.55   $118.50  
  Purchase #5 $88.43   4.811%   $92.6844   $92.68   $92.70   $92.70  
  Purchase #6 $97.46   10.837%   $108.0217   $108.02   $108.00   $108.00  
  Purchase #7 $104.85   8.398%   $113.6553   $113.66   $113.65   $113.70  
  7 purchase totals = $855.03       $924.5437   $924.55   $924.55   $924.50