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 $84.34   12.192%   $94.6227   $94.62   $94.60   $94.60  
  Purchase #2 $14.25   13.512%   $16.1755   $16.18   $16.20   $16.20  
  Purchase #3 $15.52   6.602%   $16.5446   $16.54   $16.55   $16.50  
  Purchase #4 $165.67   8.742%   $180.1529   $180.15   $180.15   $180.20  
  Purchase #5 $206.54   3.563%   $213.899   $213.90   $213.90   $213.90  
  Purchase #6 $125.33   11.292%   $139.4823   $139.48   $139.50   $139.50  
  Purchase #7 $117.90   8.616%   $128.0583   $128.06   $128.05   $128.10  
  7 purchase totals = $729.55       $788.9353   $788.93   $788.95   $789.00