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 $88.73   7.849%   $95.6944   $95.69   $95.70   $95.70  
  Purchase #2 $74.36   10.371%   $82.0719   $82.07   $82.05   $82.10  
  Purchase #3 $239.97   13.175%   $271.586   $271.59   $271.60   $271.60  
  Purchase #4 $90.70   3.463%   $93.8409   $93.84   $93.85   $93.80  
  Purchase #5 $68.67   4.292%   $71.6173   $71.62   $71.60   $71.60  
  Purchase #6 $24.89   7.482%   $26.7523   $26.75   $26.75   $26.80  
  Purchase #7 $43.72   11.831%   $48.8925   $48.89   $48.90   $48.90  
  7 purchase totals = $631.04       $690.4553   $690.45   $690.45   $690.50