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 $192.97   11.709%   $215.5649   $215.56   $215.55   $215.60  
  Purchase #2 $119.63   4.727%   $125.2849   $125.28   $125.30   $125.30  
  Purchase #3 $219.70   6.624%   $234.2529   $234.25   $234.25   $234.30  
  Purchase #4 $230.94   3.660%   $239.3924   $239.39   $239.40   $239.40  
  Purchase #5 $117.90   4.844%   $123.6111   $123.61   $123.60   $123.60  
  Purchase #6 $77.82   11.163%   $86.507   $86.51   $86.50   $86.50  
  Purchase #7 $232.47   7.548%   $250.0168   $250.02   $250.00   $250.00  
  7 purchase totals = $1,191.43       $1,274.6300   $1,274.62   $1,274.60   $1,274.70