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 $66.41   11.215%   $73.8579   $73.86   $73.85   $73.90  
  Purchase #2 $231.87   12.131%   $259.9981   $260.00   $260.00   $260.00  
  Purchase #3 $243.39   4.612%   $254.6151   $254.62   $254.60   $254.60  
  Purchase #4 $55.61   4.275%   $57.9873   $57.99   $58.00   $58.00  
  Purchase #5 $13.63   6.826%   $14.5604   $14.56   $14.55   $14.60  
  Purchase #6 $119.31   3.467%   $123.4465   $123.45   $123.45   $123.40  
  Purchase #7 $35.39   7.228%   $37.948   $37.95   $37.95   $37.90  
  7 purchase totals = $765.61       $822.4133   $822.43   $822.40   $822.40