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 $224.82   12.748%   $253.4801   $253.48   $253.50   $253.50  
  Purchase #2 $141.48   10.202%   $155.9138   $155.91   $155.90   $155.90  
  Purchase #3 $43.31   7.551%   $46.5803   $46.58   $46.60   $46.60  
  Purchase #4 $250.78   3.257%   $258.9479   $258.95   $258.95   $258.90  
  Purchase #5 $5.86   9.519%   $6.4178   $6.42   $6.40   $6.40  
  Purchase #6 $200.29   8.428%   $217.1704   $217.17   $217.15   $217.20  
  Purchase #7 $196.51   4.674%   $205.6949   $205.69   $205.70   $205.70  
  7 purchase totals = $1,063.05       $1,144.2052   $1,144.20   $1,144.20   $1,144.20