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 $113.49   6.695%   $121.0882   $121.09   $121.10   $121.10  
  Purchase #2 $103.37   6.203%   $109.782   $109.78   $109.80   $109.80  
  Purchase #3 $121.95   5.302%   $128.4158   $128.42   $128.40   $128.40  
  Purchase #4 $159.90   5.872%   $169.2893   $169.29   $169.30   $169.30  
  Purchase #5 $15.84   3.412%   $16.3805   $16.38   $16.40   $16.40  
  Purchase #6 $49.79   3.667%   $51.6158   $51.62   $51.60   $51.60  
  Purchase #7 $216.37   10.425%   $238.9266   $238.93   $238.95   $238.90  
  7 purchase totals = $780.71       $835.4982   $835.51   $835.55   $835.50