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 $172.79   5.710%   $182.6563   $182.66   $182.65   $182.70  
  Purchase #2 $193.65   6.702%   $206.6284   $206.63   $206.65   $206.60  
  Purchase #3 $125.32   4.494%   $130.9519   $130.95   $130.95   $131.00  
  Purchase #4 $190.47   4.711%   $199.443   $199.44   $199.45   $199.40  
  Purchase #5 $118.78   3.108%   $122.4717   $122.47   $122.45   $122.50  
  Purchase #6 $175.89   3.833%   $182.6319   $182.63   $182.65   $182.60  
  Purchase #7 $22.84   9.146%   $24.9289   $24.93   $24.95   $24.90  
  7 purchase totals = $999.74       $1,049.7121   $1,049.71   $1,049.75   $1,049.70