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 $247.98   10.335%   $273.6087   $273.61   $273.60   $273.60  
  Purchase #2 $101.94   9.548%   $111.6732   $111.67   $111.65   $111.70  
  Purchase #3 $216.99   10.727%   $240.2665   $240.27   $240.25   $240.30  
  Purchase #4 $220.37   9.701%   $241.7481   $241.75   $241.75   $241.70  
  Purchase #5 $20.78   7.772%   $22.395   $22.40   $22.40   $22.40  
  Purchase #6 $172.97   4.545%   $180.8315   $180.83   $180.85   $180.80  
  Purchase #7 $175.46   11.526%   $195.6835   $195.68   $195.70   $195.70  
  7 purchase totals = $1,156.49       $1,266.2065   $1,266.21   $1,266.20   $1,266.20