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 $198.87   4.863%   $208.541   $208.54   $208.55   $208.50  
  Purchase #2 $184.69   8.175%   $199.7884   $199.79   $199.80   $199.80  
  Purchase #3 $82.90   12.494%   $93.2575   $93.26   $93.25   $93.30  
  Purchase #4 $145.40   11.440%   $162.0338   $162.03   $162.05   $162.00  
  Purchase #5 $35.91   11.719%   $40.1183   $40.12   $40.10   $40.10  
  Purchase #6 $117.74   7.714%   $126.8225   $126.82   $126.80   $126.80  
  Purchase #7 $30.79   7.771%   $33.1827   $33.18   $33.20   $33.20  
  7 purchase totals = $796.30       $863.7442   $863.74   $863.75   $863.70