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 $65.35   8.484%   $70.8943   $70.89   $70.90   $70.90  
  Purchase #2 $6.66   10.425%   $7.3543   $7.35   $7.35   $7.40  
  Purchase #3 $14.44   7.648%   $15.5444   $15.54   $15.55   $15.50  
  Purchase #4 $244.50   5.269%   $257.3827   $257.38   $257.40   $257.40  
  Purchase #5 $169.85   11.160%   $188.8053   $188.81   $188.80   $188.80  
  Purchase #6 $132.63   10.606%   $146.6967   $146.70   $146.70   $146.70  
  Purchase #7 $70.36   8.442%   $76.2998   $76.30   $76.30   $76.30  
  7 purchase totals = $703.79       $762.9775   $762.97   $763.00   $763.00