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 $240.42   11.118%   $267.1499   $267.15   $267.15   $267.10  
  Purchase #2 $182.88   5.468%   $192.8799   $192.88   $192.90   $192.90  
  Purchase #3 $248.82   4.643%   $260.3727   $260.37   $260.35   $260.40  
  Purchase #4 $68.97   10.821%   $76.4332   $76.43   $76.45   $76.40  
  Purchase #5 $139.65   11.776%   $156.0952   $156.10   $156.10   $156.10  
  Purchase #6 $119.42   7.360%   $128.2093   $128.21   $128.20   $128.20  
  Purchase #7 $183.28   4.157%   $190.8989   $190.90   $190.90   $190.90  
  7 purchase totals = $1,183.44       $1,272.0391   $1,272.04   $1,272.05   $1,272.00