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 $227.69   11.772%   $254.4937   $254.49   $254.50   $254.50  
  Purchase #2 $236.79   8.119%   $256.015   $256.02   $256.00   $256.00  
  Purchase #3 $160.82   9.484%   $176.0722   $176.07   $176.05   $176.10  
  Purchase #4 $197.36   9.750%   $216.6026   $216.60   $216.60   $216.60  
  Purchase #5 $147.86   13.777%   $168.2307   $168.23   $168.25   $168.20  
  Purchase #6 $231.28   9.151%   $252.4444   $252.44   $252.45   $252.40  
  Purchase #7 $96.82   13.633%   $110.0195   $110.02   $110.00   $110.00  
  7 purchase totals = $1,298.62       $1,433.8781   $1,433.87   $1,433.85   $1,433.80