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 $204.84   8.129%   $221.4914   $221.49   $221.50   $221.50  
  Purchase #2 $140.94   7.741%   $151.8502   $151.85   $151.85   $151.90  
  Purchase #3 $36.50   11.466%   $40.6851   $40.69   $40.70   $40.70  
  Purchase #4 $16.79   5.798%   $17.7635   $17.76   $17.75   $17.80  
  Purchase #5 $225.70   7.498%   $242.623   $242.62   $242.60   $242.60  
  Purchase #6 $17.65   10.433%   $19.4914   $19.49   $19.50   $19.50  
  Purchase #7 $21.59   6.791%   $23.0562   $23.06   $23.05   $23.10  
  7 purchase totals = $664.01       $716.9608   $716.96   $716.95   $717.10