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 $88.57   9.207%   $96.7246   $96.72   $96.70   $96.70  
  Purchase #2 $250.33   6.134%   $265.6852   $265.69   $265.70   $265.70  
  Purchase #3 $197.59   4.189%   $205.867   $205.87   $205.85   $205.90  
  Purchase #4 $200.27   13.760%   $227.8272   $227.83   $227.85   $227.80  
  Purchase #5 $157.47   8.388%   $170.6786   $170.68   $170.70   $170.70  
  Purchase #6 $46.72   7.345%   $50.1516   $50.15   $50.15   $50.20  
  Purchase #7 $225.28   10.208%   $248.2766   $248.28   $248.30   $248.30  
  7 purchase totals = $1,166.23       $1,265.2108   $1,265.22   $1,265.25   $1,265.30