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 $42.74   3.542%   $44.2539   $44.25   $44.25   $44.30  
  Purchase #2 $247.46   6.569%   $263.7156   $263.72   $263.70   $263.70  
  Purchase #3 $176.74   5.510%   $186.4784   $186.48   $186.50   $186.50  
  Purchase #4 $241.57   10.378%   $266.6401   $266.64   $266.65   $266.60  
  Purchase #5 $98.96   4.286%   $103.2014   $103.20   $103.20   $103.20  
  Purchase #6 $237.84   5.518%   $250.964   $250.96   $250.95   $251.00  
  Purchase #7 $107.73   4.553%   $112.6349   $112.63   $112.65   $112.60  
  7 purchase totals = $1,153.04       $1,227.8883   $1,227.88   $1,227.90   $1,227.90