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 $232.51   5.299%   $244.8307   $244.83   $244.85   $244.80  
  Purchase #2 $13.67   4.492%   $14.2841   $14.28   $14.30   $14.30  
  Purchase #3 $16.87   10.628%   $18.6629   $18.66   $18.65   $18.70  
  Purchase #4 $196.82   5.855%   $208.3438   $208.34   $208.35   $208.30  
  Purchase #5 $219.87   7.461%   $236.2745   $236.27   $236.25   $236.30  
  Purchase #6 $30.66   3.838%   $31.8367   $31.84   $31.85   $31.80  
  Purchase #7 $223.92   8.206%   $242.2949   $242.29   $242.30   $242.30  
  7 purchase totals = $934.32       $996.5276   $996.51   $996.55   $996.50