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 $141.82   8.634%   $154.0647   $154.06   $154.05   $154.10  
  Purchase #2 $186.29   4.665%   $194.9804   $194.98   $195.00   $195.00  
  Purchase #3 $227.69   3.655%   $236.0121   $236.01   $236.00   $236.00  
  Purchase #4 $182.78   8.834%   $198.9268   $198.93   $198.95   $198.90  
  Purchase #5 $89.31   5.353%   $94.0908   $94.09   $94.10   $94.10  
  Purchase #6 $185.97   5.554%   $196.2988   $196.30   $196.30   $196.30  
  Purchase #7 $199.74   6.840%   $213.4022   $213.40   $213.40   $213.40  
  7 purchase totals = $1,213.60       $1,287.7758   $1,287.77   $1,287.80   $1,287.80