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 $193.64   6.249%   $205.7406   $205.74   $205.75   $205.70  
  Purchase #2 $116.84   11.802%   $130.6295   $130.63   $130.65   $130.60  
  Purchase #3 $240.52   6.851%   $256.998   $257.00   $257.00   $257.00  
  Purchase #4 $245.63   3.853%   $255.0941   $255.09   $255.10   $255.10  
  Purchase #5 $103.65   13.398%   $117.537   $117.54   $117.55   $117.50  
  Purchase #6 $199.34   5.779%   $210.8599   $210.86   $210.85   $210.90  
  Purchase #7 $115.48   5.545%   $121.8834   $121.88   $121.90   $121.90  
  7 purchase totals = $1,215.10       $1,298.7425   $1,298.74   $1,298.80   $1,298.70