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 $90.96   3.620%   $94.2528   $94.25   $94.25   $94.30  
  Purchase #2 $15.97   3.547%   $16.5365   $16.54   $16.55   $16.50  
  Purchase #3 $182.37   5.248%   $191.9408   $191.94   $191.95   $191.90  
  Purchase #4 $157.97   3.105%   $162.875   $162.88   $162.90   $162.90  
  Purchase #5 $188.29   9.214%   $205.639   $205.64   $205.65   $205.60  
  Purchase #6 $167.38   4.806%   $175.4243   $175.42   $175.40   $175.40  
  Purchase #7 $62.36   9.290%   $68.1532   $68.15   $68.15   $68.20  
  7 purchase totals = $865.30       $914.8216   $914.82   $914.85   $914.80