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 $22.64   13.783%   $25.7605   $25.76   $25.75   $25.80  
  Purchase #2 $136.82   8.359%   $148.2568   $148.26   $148.25   $148.30  
  Purchase #3 $98.59   8.423%   $106.8942   $106.89   $106.90   $106.90  
  Purchase #4 $247.74   3.836%   $257.2433   $257.24   $257.25   $257.20  
  Purchase #5 $172.64   4.408%   $180.25   $180.25   $180.25   $180.30  
  Purchase #6 $180.25   10.675%   $199.4917   $199.49   $199.50   $199.50  
  Purchase #7 $110.84   6.648%   $118.2086   $118.21   $118.20   $118.20  
  7 purchase totals = $969.52       $1,036.1051   $1,036.10   $1,036.10   $1,036.20