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 $201.74   4.266%   $210.3462   $210.35   $210.35   $210.30  
  Purchase #2 $23.66   6.333%   $25.1584   $25.16   $25.15   $25.20  
  Purchase #3 $80.57   5.117%   $84.6928   $84.69   $84.70   $84.70  
  Purchase #4 $98.66   6.345%   $104.92   $104.92   $104.90   $104.90  
  Purchase #5 $223.63   8.105%   $241.7552   $241.76   $241.75   $241.80  
  Purchase #6 $102.59   11.337%   $114.2206   $114.22   $114.20   $114.20  
  Purchase #7 $224.25   7.445%   $240.9454   $240.95   $240.95   $240.90  
  7 purchase totals = $955.10       $1,022.0386   $1,022.05   $1,022.00   $1,022.00