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 $247.43   9.436%   $270.7775   $270.78   $270.80   $270.80  
  Purchase #2 $239.93   6.140%   $254.6617   $254.66   $254.65   $254.70  
  Purchase #3 $15.66   6.826%   $16.729   $16.73   $16.75   $16.70  
  Purchase #4 $233.95   6.632%   $249.4656   $249.47   $249.45   $249.50  
  Purchase #5 $217.49   10.185%   $239.6414   $239.64   $239.65   $239.60  
  Purchase #6 $138.34   4.528%   $144.604   $144.60   $144.60   $144.60  
  Purchase #7 $173.97   8.412%   $188.6044   $188.60   $188.60   $188.60  
  7 purchase totals = $1,266.77       $1,364.4836   $1,364.48   $1,364.50   $1,364.50