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 $74.81   13.208%   $84.6909   $84.69   $84.70   $84.70  
  Purchase #2 $182.36   9.239%   $199.2082   $199.21   $199.20   $199.20  
  Purchase #3 $167.61   6.345%   $178.2449   $178.24   $178.25   $178.20  
  Purchase #4 $34.30   3.744%   $35.5842   $35.58   $35.60   $35.60  
  Purchase #5 $236.40   5.586%   $249.6053   $249.61   $249.60   $249.60  
  Purchase #6 $116.90   11.264%   $130.0676   $130.07   $130.05   $130.10  
  Purchase #7 $126.73   8.182%   $137.099   $137.10   $137.10   $137.10  
  7 purchase totals = $939.11       $1,014.5001   $1,014.50   $1,014.50   $1,014.50