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 $76.33   8.675%   $82.9516   $82.95   $82.95   $83.00  
  Purchase #2 $30.46   8.553%   $33.0652   $33.07   $33.05   $33.10  
  Purchase #3 $9.31   13.316%   $10.5497   $10.55   $10.55   $10.50  
  Purchase #4 $180.66   8.391%   $195.8192   $195.82   $195.80   $195.80  
  Purchase #5 $112.74   9.782%   $123.7682   $123.77   $123.75   $123.80  
  Purchase #6 $161.29   13.648%   $183.3029   $183.30   $183.30   $183.30  
  Purchase #7 $122.93   11.389%   $136.9305   $136.93   $136.95   $136.90  
  7 purchase totals = $693.72       $766.3873   $766.39   $766.35   $766.40