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 $246.95   3.373%   $255.2796   $255.28   $255.30   $255.30  
  Purchase #2 $220.73   10.788%   $244.5424   $244.54   $244.55   $244.50  
  Purchase #3 $189.36   6.206%   $201.1117   $201.11   $201.10   $201.10  
  Purchase #4 $113.44   5.162%   $119.2958   $119.30   $119.30   $119.30  
  Purchase #5 $242.92   6.309%   $258.2458   $258.25   $258.25   $258.20  
  Purchase #6 $185.39   8.478%   $201.1074   $201.11   $201.10   $201.10  
  Purchase #7 $127.44   5.184%   $134.0465   $134.05   $134.05   $134.00  
  7 purchase totals = $1,326.23       $1,413.6292   $1,413.64   $1,413.65   $1,413.50