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 $232.25   11.812%   $259.6834   $259.68   $259.70   $259.70  
  Purchase #2 $239.57   5.757%   $253.362   $253.36   $253.35   $253.40  
  Purchase #3 $148.95   10.236%   $164.1965   $164.20   $164.20   $164.20  
  Purchase #4 $120.75   11.526%   $134.6676   $134.67   $134.65   $134.70  
  Purchase #5 $51.67   10.748%   $57.2235   $57.22   $57.20   $57.20  
  Purchase #6 $14.49   4.252%   $15.1061   $15.11   $15.10   $15.10  
  Purchase #7 $131.33   9.308%   $143.5542   $143.55   $143.55   $143.60  
  7 purchase totals = $939.01       $1,027.7933   $1,027.79   $1,027.75   $1,027.90