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 $228.89   10.316%   $252.5023   $252.50   $252.50   $252.50  
  Purchase #2 $241.68   5.489%   $254.9458   $254.95   $254.95   $254.90  
  Purchase #3 $26.60   8.481%   $28.8559   $28.86   $28.85   $28.90  
  Purchase #4 $184.94   4.230%   $192.763   $192.76   $192.75   $192.80  
  Purchase #5 $218.82   4.494%   $228.6538   $228.65   $228.65   $228.70  
  Purchase #6 $233.46   5.149%   $245.4809   $245.48   $245.50   $245.50  
  Purchase #7 $146.26   10.723%   $161.9435   $161.94   $161.95   $161.90  
  7 purchase totals = $1,280.65       $1,365.1452   $1,365.14   $1,365.15   $1,365.20