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 $82.65   12.443%   $92.9341   $92.93   $92.95   $92.90  
  Purchase #2 $81.66   13.464%   $92.6547   $92.65   $92.65   $92.70  
  Purchase #3 $162.85   3.817%   $169.066   $169.07   $169.05   $169.10  
  Purchase #4 $45.63   11.548%   $50.8994   $50.90   $50.90   $50.90  
  Purchase #5 $250.67   7.309%   $268.9915   $268.99   $269.00   $269.00  
  Purchase #6 $50.78   13.726%   $57.7501   $57.75   $57.75   $57.80  
  Purchase #7 $77.33   13.164%   $87.5097   $87.51   $87.50   $87.50  
  7 purchase totals = $751.57       $819.8055   $819.80   $819.80   $819.90