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 $126.98   3.469%   $131.3849   $131.38   $131.40   $131.40  
  Purchase #2 $9.56   4.613%   $10.001   $10.00   $10.00   $10.00  
  Purchase #3 $29.75   3.169%   $30.6928   $30.69   $30.70   $30.70  
  Purchase #4 $182.55   13.117%   $206.4951   $206.50   $206.50   $206.50  
  Purchase #5 $227.87   5.832%   $241.1594   $241.16   $241.15   $241.20  
  Purchase #6 $176.33   10.479%   $194.8076   $194.81   $194.80   $194.80  
  Purchase #7 $28.71   10.611%   $31.7564   $31.76   $31.75   $31.80  
  7 purchase totals = $781.75       $846.2972   $846.30   $846.30   $846.40