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 $59.98   4.670%   $62.7811   $62.78   $62.80   $62.80  
  Purchase #2 $145.81   8.556%   $158.2855   $158.29   $158.30   $158.30  
  Purchase #3 $52.73   13.871%   $60.0442   $60.04   $60.05   $60.00  
  Purchase #4 $73.56   3.276%   $75.9698   $75.97   $75.95   $76.00  
  Purchase #5 $56.30   8.433%   $61.0478   $61.05   $61.05   $61.00  
  Purchase #6 $214.40   12.548%   $241.3029   $241.30   $241.30   $241.30  
  Purchase #7 $167.96   10.288%   $185.2397   $185.24   $185.25   $185.20  
  7 purchase totals = $770.74       $844.6710   $844.67   $844.70   $844.60