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 $227.69   5.861%   $241.0349   $241.03   $241.05   $241.00  
  Purchase #2 $210.40   7.521%   $226.2242   $226.22   $226.20   $226.20  
  Purchase #3 $142.27   6.104%   $150.9542   $150.95   $150.95   $151.00  
  Purchase #4 $221.35   12.218%   $248.3945   $248.39   $248.40   $248.40  
  Purchase #5 $199.47   8.579%   $216.5825   $216.58   $216.60   $216.60  
  Purchase #6 $174.71   12.476%   $196.5068   $196.51   $196.50   $196.50  
  Purchase #7 $207.64   4.667%   $217.3306   $217.33   $217.35   $217.30  
  7 purchase totals = $1,383.53       $1,497.0277   $1,497.01   $1,497.05   $1,497.00