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 $77.45   10.116%   $85.2848   $85.28   $85.30   $85.30  
  Purchase #2 $13.41   5.593%   $14.16   $14.16   $14.15   $14.20  
  Purchase #3 $61.44   5.260%   $64.6717   $64.67   $64.65   $64.70  
  Purchase #4 $159.50   3.561%   $165.1798   $165.18   $165.20   $165.20  
  Purchase #5 $93.87   9.465%   $102.7548   $102.75   $102.75   $102.80  
  Purchase #6 $74.65   6.704%   $79.6545   $79.65   $79.65   $79.70  
  Purchase #7 $236.50   8.485%   $256.567   $256.57   $256.55   $256.60  
  7 purchase totals = $716.82       $768.2726   $768.26   $768.25   $768.50