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 $91.71   6.313%   $97.4997   $97.50   $97.50   $97.50  
  Purchase #2 $67.72   9.260%   $73.9909   $73.99   $74.00   $74.00  
  Purchase #3 $162.31   6.726%   $173.227   $173.23   $173.25   $173.20  
  Purchase #4 $250.37   3.755%   $259.7714   $259.77   $259.75   $259.80  
  Purchase #5 $166.83   13.582%   $189.4889   $189.49   $189.50   $189.50  
  Purchase #6 $173.48   8.553%   $188.3177   $188.32   $188.30   $188.30  
  Purchase #7 $155.29   8.798%   $168.9524   $168.95   $168.95   $169.00  
  7 purchase totals = $1,067.71       $1,151.2480   $1,151.25   $1,151.25   $1,151.30