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 $95.27   3.116%   $98.2386   $98.24   $98.25   $98.20  
  Purchase #2 $117.35   13.789%   $133.5314   $133.53   $133.55   $133.50  
  Purchase #3 $79.25   6.260%   $84.2111   $84.21   $84.20   $84.20  
  Purchase #4 $64.94   6.252%   $69   $69.00   $69.00   $69.00  
  Purchase #5 $107.98   6.568%   $115.0721   $115.07   $115.05   $115.10  
  Purchase #6 $150.63   7.190%   $161.4603   $161.46   $161.45   $161.50  
  Purchase #7 $57.25   6.228%   $60.8155   $60.82   $60.80   $60.80  
  7 purchase totals = $672.67       $722.3290   $722.33   $722.30   $722.30