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 $24.66   3.757%   $25.5865   $25.59   $25.60   $25.60  
  Purchase #2 $95.67   13.453%   $108.5405   $108.54   $108.55   $108.50  
  Purchase #3 $47.86   3.607%   $49.5863   $49.59   $49.60   $49.60  
  Purchase #4 $159.33   10.199%   $175.5801   $175.58   $175.60   $175.60  
  Purchase #5 $64.54   10.478%   $71.3025   $71.30   $71.30   $71.30  
  Purchase #6 $154.42   9.817%   $169.5794   $169.58   $169.60   $169.60  
  Purchase #7 $161.34   4.420%   $168.4712   $168.47   $168.45   $168.50  
  7 purchase totals = $707.82       $768.6465   $768.65   $768.70   $768.70