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 $215.32   4.113%   $224.1761   $224.18   $224.20   $224.20  
  Purchase #2 $51.46   6.777%   $54.9474   $54.95   $54.95   $54.90  
  Purchase #3 $56.55   11.707%   $63.1703   $63.17   $63.15   $63.20  
  Purchase #4 $183.54   6.765%   $195.9565   $195.96   $195.95   $196.00  
  Purchase #5 $158.77   11.500%   $177.0286   $177.03   $177.05   $177.00  
  Purchase #6 $42.54   11.235%   $47.3194   $47.32   $47.30   $47.30  
  Purchase #7 $250.94   11.176%   $278.9851   $278.99   $279.00   $279.00  
  7 purchase totals = $959.12       $1,041.5834   $1,041.60   $1,041.60   $1,041.60