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 $134.27   11.140%   $149.2277   $149.23   $149.25   $149.20  
  Purchase #2 $214.92   3.228%   $221.8576   $221.86   $221.85   $221.90  
  Purchase #3 $130.28   3.467%   $134.7968   $134.80   $134.80   $134.80  
  Purchase #4 $65.82   11.431%   $73.3439   $73.34   $73.35   $73.30  
  Purchase #5 $192.62   7.444%   $206.9586   $206.96   $206.95   $207.00  
  Purchase #6 $83.78   5.589%   $88.4625   $88.46   $88.45   $88.50  
  Purchase #7 $151.46   4.585%   $158.4044   $158.40   $158.40   $158.40  
  7 purchase totals = $973.15       $1,033.0515   $1,033.05   $1,033.05   $1,033.10