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 $178.99   13.194%   $202.6059   $202.61   $202.60   $202.60  
  Purchase #2 $151.54   10.833%   $167.9563   $167.96   $167.95   $168.00  
  Purchase #3 $57.45   13.660%   $65.2977   $65.30   $65.30   $65.30  
  Purchase #4 $108.44   13.778%   $123.3809   $123.38   $123.40   $123.40  
  Purchase #5 $14.78   10.252%   $16.2952   $16.30   $16.30   $16.30  
  Purchase #6 $67.58   12.414%   $75.9694   $75.97   $75.95   $76.00  
  Purchase #7 $204.69   6.546%   $218.089   $218.09   $218.10   $218.10  
  7 purchase totals = $783.47       $869.5944   $869.61   $869.60   $869.70