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 $92.41   7.307%   $99.1624   $99.16   $99.15   $99.20  
  Purchase #2 $214.38   11.867%   $239.8205   $239.82   $239.80   $239.80  
  Purchase #3 $250.48   8.179%   $270.9668   $270.97   $270.95   $271.00  
  Purchase #4 $163.44   7.461%   $175.6343   $175.63   $175.65   $175.60  
  Purchase #5 $149.73   12.605%   $168.6035   $168.60   $168.60   $168.60  
  Purchase #6 $151.89   11.507%   $169.368   $169.37   $169.35   $169.40  
  Purchase #7 $229.71   3.167%   $236.9849   $236.98   $237.00   $237.00  
  7 purchase totals = $1,252.04       $1,360.5404   $1,360.53   $1,360.50   $1,360.60