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 $24.36   10.854%   $27.004   $27.00   $27.00   $27.00  
  Purchase #2 $244.40   6.158%   $259.4502   $259.45   $259.45   $259.50  
  Purchase #3 $39.69   6.633%   $42.3226   $42.32   $42.30   $42.30  
  Purchase #4 $184.59   12.118%   $206.9586   $206.96   $206.95   $207.00  
  Purchase #5 $119.37   12.157%   $133.8818   $133.88   $133.90   $133.90  
  Purchase #6 $209.65   7.191%   $224.7259   $224.73   $224.75   $224.70  
  Purchase #7 $214.40   11.749%   $239.5899   $239.59   $239.60   $239.60  
  7 purchase totals = $1,036.46       $1,133.9330   $1,133.93   $1,133.95   $1,134.00