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 $204.60   6.117%   $217.1154   $217.12   $217.10   $217.10  
  Purchase #2 $244.98   7.153%   $262.5034   $262.50   $262.50   $262.50  
  Purchase #3 $33.55   3.605%   $34.7595   $34.76   $34.75   $34.80  
  Purchase #4 $45.76   13.358%   $51.8726   $51.87   $51.85   $51.90  
  Purchase #5 $88.29   5.813%   $93.4223   $93.42   $93.40   $93.40  
  Purchase #6 $35.44   13.549%   $40.2418   $40.24   $40.25   $40.20  
  Purchase #7 $130.48   9.223%   $142.5142   $142.51   $142.50   $142.50  
  7 purchase totals = $783.10       $842.4292   $842.42   $842.35   $842.40