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 $249.82   3.686%   $259.0284   $259.03   $259.05   $259.00  
  Purchase #2 $86.99   12.207%   $97.6089   $97.61   $97.60   $97.60  
  Purchase #3 $160.70   10.525%   $177.6137   $177.61   $177.60   $177.60  
  Purchase #4 $13.53   7.762%   $14.5802   $14.58   $14.60   $14.60  
  Purchase #5 $162.78   10.654%   $180.1226   $180.12   $180.10   $180.10  
  Purchase #6 $244.63   11.235%   $272.1142   $272.11   $272.10   $272.10  
  Purchase #7 $199.80   7.584%   $214.9528   $214.95   $214.95   $215.00  
  7 purchase totals = $1,118.25       $1,216.0208   $1,216.01   $1,216.00   $1,216.00