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 $153.49   12.859%   $173.2273   $173.23   $173.25   $173.20  
  Purchase #2 $238.98   5.623%   $252.4178   $252.42   $252.40   $252.40  
  Purchase #3 $217.90   12.517%   $245.1745   $245.17   $245.15   $245.20  
  Purchase #4 $60.63   9.823%   $66.5857   $66.59   $66.60   $66.60  
  Purchase #5 $81.38   5.697%   $86.0162   $86.02   $86.00   $86.00  
  Purchase #6 $182.41   7.809%   $196.6544   $196.65   $196.65   $196.70  
  Purchase #7 $51.65   4.584%   $54.0176   $54.02   $54.00   $54.00  
  7 purchase totals = $986.44       $1,074.0935   $1,074.10   $1,074.05   $1,074.10