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 $66.75   11.569%   $74.4723   $74.47   $74.45   $74.50  
  Purchase #2 $90.92   11.581%   $101.4494   $101.45   $101.45   $101.40  
  Purchase #3 $165.38   5.618%   $174.671   $174.67   $174.65   $174.70  
  Purchase #4 $37.25   7.512%   $40.0482   $40.05   $40.05   $40.00  
  Purchase #5 $226.51   8.409%   $245.5572   $245.56   $245.55   $245.60  
  Purchase #6 $11.83   9.616%   $12.9676   $12.97   $12.95   $13.00  
  Purchase #7 $240.36   3.665%   $249.1692   $249.17   $249.15   $249.20  
  7 purchase totals = $839.00       $898.3349   $898.34   $898.25   $898.40