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 $182.99   10.343%   $201.9167   $201.92   $201.90   $201.90  
  Purchase #2 $237.69   12.460%   $267.3062   $267.31   $267.30   $267.30  
  Purchase #3 $65.81   11.570%   $73.4242   $73.42   $73.40   $73.40  
  Purchase #4 $157.34   10.583%   $173.9913   $173.99   $174.00   $174.00  
  Purchase #5 $8.53   8.754%   $9.2767   $9.28   $9.30   $9.30  
  Purchase #6 $44.51   6.576%   $47.437   $47.44   $47.45   $47.40  
  Purchase #7 $7.54   8.505%   $8.1813   $8.18   $8.20   $8.20  
  7 purchase totals = $704.41       $781.5334   $781.54   $781.55   $781.50