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 $136.58   5.486%   $144.0728   $144.07   $144.05   $144.10  
  Purchase #2 $214.98   4.287%   $224.1962   $224.20   $224.20   $224.20  
  Purchase #3 $167.38   3.584%   $173.3789   $173.38   $173.40   $173.40  
  Purchase #4 $180.80   8.370%   $195.933   $195.93   $195.95   $195.90  
  Purchase #5 $204.33   6.631%   $217.8791   $217.88   $217.90   $217.90  
  Purchase #6 $145.85   7.154%   $156.2841   $156.28   $156.30   $156.30  
  Purchase #7 $200.73   5.209%   $211.186   $211.19   $211.20   $211.20  
  7 purchase totals = $1,250.65       $1,322.9301   $1,322.93   $1,323.00   $1,323.00