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 $110.72   3.189%   $114.2509   $114.25   $114.25   $114.30  
  Purchase #2 $219.27   11.596%   $244.6965   $244.70   $244.70   $244.70  
  Purchase #3 $198.58   9.396%   $217.2386   $217.24   $217.25   $217.20  
  Purchase #4 $172.44   6.458%   $183.5762   $183.58   $183.60   $183.60  
  Purchase #5 $233.57   4.676%   $244.4917   $244.49   $244.50   $244.50  
  Purchase #6 $202.89   10.471%   $224.1346   $224.13   $224.15   $224.10  
  Purchase #7 $31.90   12.591%   $35.9165   $35.92   $35.90   $35.90  
  7 purchase totals = $1,169.37       $1,264.3050   $1,264.31   $1,264.35   $1,264.30