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 $114.91   3.282%   $118.6813   $118.68   $118.70   $118.70  
  Purchase #2 $8.67   7.382%   $9.31   $9.31   $9.30   $9.30  
  Purchase #3 $16.72   4.826%   $17.5269   $17.53   $17.55   $17.50  
  Purchase #4 $59.66   8.582%   $64.78   $64.78   $64.80   $64.80  
  Purchase #5 $168.50   13.711%   $191.603   $191.60   $191.60   $191.60  
  Purchase #6 $162.93   8.206%   $176.3   $176.30   $176.30   $176.30  
  Purchase #7 $128.30   5.652%   $135.5515   $135.55   $135.55   $135.60  
  7 purchase totals = $659.69       $713.7527   $713.75   $713.80   $713.80