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 $85.39   9.248%   $93.2869   $93.29   $93.30   $93.30  
  Purchase #2 $62.98   3.172%   $64.9777   $64.98   $65.00   $65.00  
  Purchase #3 $146.75   4.662%   $153.5915   $153.59   $153.60   $153.60  
  Purchase #4 $236.63   3.431%   $244.7488   $244.75   $244.75   $244.70  
  Purchase #5 $129.37   3.516%   $133.9186   $133.92   $133.90   $133.90  
  Purchase #6 $174.83   10.387%   $192.9896   $192.99   $193.00   $193.00  
  Purchase #7 $248.88   10.207%   $274.2832   $274.28   $274.30   $274.30  
  7 purchase totals = $1,084.83       $1,157.7963   $1,157.80   $1,157.85   $1,157.80