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 $119.63   4.164%   $124.6114   $124.61   $124.60   $124.60  
  Purchase #2 $36.37   11.264%   $40.4667   $40.47   $40.45   $40.50  
  Purchase #3 $32.45   7.732%   $34.959   $34.96   $34.95   $35.00  
  Purchase #4 $139.59   5.532%   $147.3121   $147.31   $147.30   $147.30  
  Purchase #5 $70.30   5.169%   $73.9338   $73.93   $73.95   $73.90  
  Purchase #6 $49.55   3.615%   $51.3412   $51.34   $51.35   $51.30  
  Purchase #7 $242.65   3.536%   $251.2301   $251.23   $251.25   $251.20  
  7 purchase totals = $690.54       $723.8543   $723.85   $723.85   $723.80