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 $243.92   12.234%   $273.7612   $273.76   $273.75   $273.80  
  Purchase #2 $220.88   13.170%   $249.9699   $249.97   $249.95   $250.00  
  Purchase #3 $20.97   13.292%   $23.7573   $23.76   $23.75   $23.80  
  Purchase #4 $242.83   8.347%   $263.099   $263.10   $263.10   $263.10  
  Purchase #5 $34.59   7.742%   $37.268   $37.27   $37.25   $37.30  
  Purchase #6 $65.84   5.345%   $69.3591   $69.36   $69.35   $69.40  
  Purchase #7 $184.54   4.531%   $192.9015   $192.90   $192.90   $192.90  
  7 purchase totals = $1,013.57       $1,110.1160   $1,110.12   $1,110.05   $1,110.30