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 $25.62   5.166%   $26.9435   $26.94   $26.95   $26.90  
  Purchase #2 $206.84   13.591%   $234.9516   $234.95   $234.95   $235.00  
  Purchase #3 $130.98   8.383%   $141.9601   $141.96   $141.95   $142.00  
  Purchase #4 $44.41   7.315%   $47.6586   $47.66   $47.65   $47.70  
  Purchase #5 $154.50   3.479%   $159.8751   $159.88   $159.90   $159.90  
  Purchase #6 $222.49   12.189%   $249.6093   $249.61   $249.60   $249.60  
  Purchase #7 $229.53   10.596%   $253.851   $253.85   $253.85   $253.90  
  7 purchase totals = $1,014.37       $1,114.8492   $1,114.85   $1,114.85   $1,115.00