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 $79.49   7.709%   $85.6179   $85.62   $85.60   $85.60  
  Purchase #2 $141.48   9.208%   $154.5075   $154.51   $154.50   $154.50  
  Purchase #3 $184.94   9.197%   $201.9489   $201.95   $201.95   $201.90  
  Purchase #4 $146.77   3.534%   $151.9569   $151.96   $151.95   $152.00  
  Purchase #5 $228.51   13.509%   $259.3794   $259.38   $259.40   $259.40  
  Purchase #6 $192.60   13.149%   $217.925   $217.93   $217.95   $217.90  
  Purchase #7 $120.90   13.823%   $137.612   $137.61   $137.60   $137.60  
  7 purchase totals = $1,094.69       $1,208.9476   $1,208.96   $1,208.95   $1,208.90