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 $17.69   8.292%   $19.1569   $19.16   $19.15   $19.20  
  Purchase #2 $87.58   6.182%   $92.9942   $92.99   $93.00   $93.00  
  Purchase #3 $169.25   4.434%   $176.7545   $176.75   $176.75   $176.80  
  Purchase #4 $121.54   7.104%   $130.1742   $130.17   $130.15   $130.20  
  Purchase #5 $147.87   7.861%   $159.4941   $159.49   $159.50   $159.50  
  Purchase #6 $202.70   5.418%   $213.6823   $213.68   $213.70   $213.70  
  Purchase #7 $109.98   5.146%   $115.6396   $115.64   $115.65   $115.60  
  7 purchase totals = $856.61       $907.8958   $907.88   $907.90   $908.00