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 $146.87   13.686%   $166.9706   $166.97   $166.95   $167.00  
  Purchase #2 $28.95   8.468%   $31.4015   $31.40   $31.40   $31.40  
  Purchase #3 $192.62   4.347%   $200.9932   $200.99   $201.00   $201.00  
  Purchase #4 $157.31   4.472%   $164.3449   $164.34   $164.35   $164.30  
  Purchase #5 $14.32   9.807%   $15.7244   $15.72   $15.70   $15.70  
  Purchase #6 $194.97   6.676%   $207.9862   $207.99   $208.00   $208.00  
  Purchase #7 $87.87   13.560%   $99.7852   $99.79   $99.80   $99.80  
  7 purchase totals = $822.91       $887.2060   $887.20   $887.20   $887.20