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 $186.28   8.159%   $201.4786   $201.48   $201.50   $201.50  
  Purchase #2 $13.85   9.711%   $15.195   $15.20   $15.20   $15.20  
  Purchase #3 $225.98   8.306%   $244.7499   $244.75   $244.75   $244.70  
  Purchase #4 $14.82   8.317%   $16.0526   $16.05   $16.05   $16.10  
  Purchase #5 $95.37   10.669%   $105.545   $105.55   $105.55   $105.50  
  Purchase #6 $101.50   13.428%   $115.1294   $115.13   $115.15   $115.10  
  Purchase #7 $185.97   7.313%   $199.57   $199.57   $199.55   $199.60  
  7 purchase totals = $823.77       $897.7205   $897.73   $897.75   $897.70