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 $242.63   5.571%   $256.1469   $256.15   $256.15   $256.10  
  Purchase #2 $127.91   5.339%   $134.7391   $134.74   $134.75   $134.70  
  Purchase #3 $231.79   4.120%   $241.3397   $241.34   $241.35   $241.30  
  Purchase #4 $92.62   7.163%   $99.2544   $99.25   $99.25   $99.30  
  Purchase #5 $217.86   4.537%   $227.7443   $227.74   $227.75   $227.70  
  Purchase #6 $158.89   10.326%   $175.297   $175.30   $175.30   $175.30  
  Purchase #7 $29.31   5.807%   $31.012   $31.01   $31.00   $31.00  
  7 purchase totals = $1,101.01       $1,165.5334   $1,165.53   $1,165.55   $1,165.40