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 $85.41   13.381%   $96.8387   $96.84   $96.85   $96.80  
  Purchase #2 $33.57   7.559%   $36.1076   $36.11   $36.10   $36.10  
  Purchase #3 $46.55   4.754%   $48.763   $48.76   $48.75   $48.80  
  Purchase #4 $33.66   10.335%   $37.1388   $37.14   $37.15   $37.10  
  Purchase #5 $121.65   6.785%   $129.904   $129.90   $129.90   $129.90  
  Purchase #6 $154.62   12.529%   $173.9923   $173.99   $174.00   $174.00  
  Purchase #7 $36.90   8.583%   $40.0671   $40.07   $40.05   $40.10  
  7 purchase totals = $512.36       $562.8115   $562.81   $562.80   $562.80