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 $56.87   4.814%   $59.6077   $59.61   $59.60   $59.60  
  Purchase #2 $120.99   13.191%   $136.9498   $136.95   $136.95   $136.90  
  Purchase #3 $109.59   13.264%   $124.126   $124.13   $124.15   $124.10  
  Purchase #4 $239.86   4.131%   $249.7686   $249.77   $249.75   $249.80  
  Purchase #5 $148.76   10.334%   $164.1329   $164.13   $164.15   $164.10  
  Purchase #6 $241.57   9.687%   $264.9709   $264.97   $264.95   $265.00  
  Purchase #7 $153.71   11.310%   $171.0946   $171.09   $171.10   $171.10  
  7 purchase totals = $1,071.35       $1,170.6505   $1,170.65   $1,170.65   $1,170.60