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 $59.61   3.808%   $61.8799   $61.88   $61.90   $61.90  
  Purchase #2 $161.68   8.469%   $175.3727   $175.37   $175.35   $175.40  
  Purchase #3 $204.87   6.802%   $218.8053   $218.81   $218.80   $218.80  
  Purchase #4 $93.42   5.542%   $98.5973   $98.60   $98.60   $98.60  
  Purchase #5 $94.34   5.229%   $99.273   $99.27   $99.25   $99.30  
  Purchase #6 $187.73   11.250%   $208.8496   $208.85   $208.85   $208.80  
  Purchase #7 $43.30   6.750%   $46.2228   $46.22   $46.20   $46.20  
  7 purchase totals = $844.95       $909.0006   $909.00   $908.95   $909.00