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 $17.93   11.247%   $19.9466   $19.95   $19.95   $19.90  
  Purchase #2 $184.34   12.265%   $206.9493   $206.95   $206.95   $206.90  
  Purchase #3 $155.44   5.690%   $164.2845   $164.28   $164.30   $164.30  
  Purchase #4 $248.60   7.303%   $266.7553   $266.76   $266.75   $266.80  
  Purchase #5 $24.61   8.606%   $26.7279   $26.73   $26.75   $26.70  
  Purchase #6 $80.67   12.579%   $90.8175   $90.82   $90.80   $90.80  
  Purchase #7 $173.78   9.108%   $189.6079   $189.61   $189.60   $189.60  
  7 purchase totals = $885.37       $965.0890   $965.10   $965.10   $965.00