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 $242.57   10.715%   $268.5614   $268.56   $268.55   $268.60  
  Purchase #2 $209.60   11.301%   $233.2869   $233.29   $233.30   $233.30  
  Purchase #3 $36.48   7.291%   $39.1398   $39.14   $39.15   $39.10  
  Purchase #4 $213.41   7.597%   $229.6228   $229.62   $229.60   $229.60  
  Purchase #5 $45.77   4.621%   $47.885   $47.89   $47.90   $47.90  
  Purchase #6 $72.36   4.782%   $75.8203   $75.82   $75.80   $75.80  
  Purchase #7 $227.38   7.523%   $244.4858   $244.49   $244.50   $244.50  
  7 purchase totals = $1,047.57       $1,138.8020   $1,138.81   $1,138.80   $1,138.80