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 $192.66   11.651%   $215.1068   $215.11   $215.10   $215.10  
  Purchase #2 $112.72   11.458%   $125.6355   $125.64   $125.65   $125.60  
  Purchase #3 $209.54   5.833%   $221.7625   $221.76   $221.75   $221.80  
  Purchase #4 $125.26   5.473%   $132.1155   $132.12   $132.10   $132.10  
  Purchase #5 $231.32   4.133%   $240.8805   $240.88   $240.90   $240.90  
  Purchase #6 $86.61   12.305%   $97.2674   $97.27   $97.25   $97.30  
  Purchase #7 $9.73   6.558%   $10.3681   $10.37   $10.35   $10.40  
  7 purchase totals = $967.84       $1,043.1363   $1,043.15   $1,043.10   $1,043.20