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 $226.97   9.624%   $248.8136   $248.81   $248.80   $248.80  
  Purchase #2 $13.79   3.378%   $14.2558   $14.26   $14.25   $14.30  
  Purchase #3 $108.47   10.415%   $119.7672   $119.77   $119.75   $119.80  
  Purchase #4 $244.38   13.134%   $276.4769   $276.48   $276.50   $276.50  
  Purchase #5 $11.85   3.673%   $12.2853   $12.29   $12.30   $12.30  
  Purchase #6 $117.26   13.487%   $133.0749   $133.07   $133.05   $133.10  
  Purchase #7 $150.85   5.215%   $158.7168   $158.72   $158.70   $158.70  
  7 purchase totals = $873.57       $963.3905   $963.40   $963.35   $963.50