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 $223.42   5.699%   $236.1527   $236.15   $236.15   $236.20  
  Purchase #2 $41.37   11.242%   $46.0208   $46.02   $46.00   $46.00  
  Purchase #3 $117.99   10.379%   $130.2362   $130.24   $130.25   $130.20  
  Purchase #4 $204.60   5.266%   $215.3742   $215.37   $215.35   $215.40  
  Purchase #5 $94.90   4.862%   $99.514   $99.51   $99.50   $99.50  
  Purchase #6 $227.27   10.318%   $250.7197   $250.72   $250.70   $250.70  
  Purchase #7 $241.85   10.395%   $266.9903   $266.99   $267.00   $267.00  
  7 purchase totals = $1,151.40       $1,245.0079   $1,245.00   $1,244.95   $1,245.00