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 $176.58   9.491%   $193.3392   $193.34   $193.35   $193.30  
  Purchase #2 $8.93   7.712%   $9.6187   $9.62   $9.60   $9.60  
  Purchase #3 $65.89   11.181%   $73.2572   $73.26   $73.25   $73.30  
  Purchase #4 $60.98   10.543%   $67.4091   $67.41   $67.40   $67.40  
  Purchase #5 $173.56   7.107%   $185.8949   $185.89   $185.90   $185.90  
  Purchase #6 $127.44   7.811%   $137.3943   $137.39   $137.40   $137.40  
  Purchase #7 $185.98   6.776%   $198.582   $198.58   $198.60   $198.60  
  7 purchase totals = $799.36       $865.4954   $865.49   $865.50   $865.50