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 $88.84   3.592%   $92.0311   $92.03   $92.05   $92.00  
  Purchase #2 $111.84   4.104%   $116.4299   $116.43   $116.45   $116.40  
  Purchase #3 $118.87   5.736%   $125.6884   $125.69   $125.70   $125.70  
  Purchase #4 $19.65   3.497%   $20.3372   $20.34   $20.35   $20.30  
  Purchase #5 $248.30   12.742%   $279.9384   $279.94   $279.95   $279.90  
  Purchase #6 $132.78   6.259%   $141.0907   $141.09   $141.10   $141.10  
  Purchase #7 $49.26   3.272%   $50.8718   $50.87   $50.85   $50.90  
  7 purchase totals = $769.54       $826.3875   $826.39   $826.45   $826.30