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 $245.95   9.162%   $268.4839   $268.48   $268.50   $268.50  
  Purchase #2 $192.64   3.209%   $198.8218   $198.82   $198.80   $198.80  
  Purchase #3 $50.78   4.743%   $53.1885   $53.19   $53.20   $53.20  
  Purchase #4 $158.51   7.614%   $170.579   $170.58   $170.60   $170.60  
  Purchase #5 $129.97   5.657%   $137.3224   $137.32   $137.30   $137.30  
  Purchase #6 $10.63   8.262%   $11.5083   $11.51   $11.50   $11.50  
  Purchase #7 $173.65   9.835%   $190.7285   $190.73   $190.75   $190.70  
  7 purchase totals = $962.13       $1,030.6324   $1,030.63   $1,030.65   $1,030.60