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 $22.77   5.653%   $24.0572   $24.06   $24.05   $24.10  
  Purchase #2 $14.94   9.402%   $16.3447   $16.34   $16.35   $16.30  
  Purchase #3 $195.33   9.371%   $213.6344   $213.63   $213.65   $213.60  
  Purchase #4 $159.85   5.467%   $168.589   $168.59   $168.60   $168.60  
  Purchase #5 $23.82   3.531%   $24.6611   $24.66   $24.65   $24.70  
  Purchase #6 $114.77   4.102%   $119.4779   $119.48   $119.50   $119.50  
  Purchase #7 $128.26   3.701%   $133.0069   $133.01   $133.00   $133.00  
  7 purchase totals = $659.74       $699.7712   $699.77   $699.80   $699.80