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 $87.91   11.443%   $97.9695   $97.97   $97.95   $98.00  
  Purchase #2 $239.78   13.244%   $271.5365   $271.54   $271.55   $271.50  
  Purchase #3 $173.87   13.307%   $197.0069   $197.01   $197.00   $197.00  
  Purchase #4 $145.69   4.861%   $152.772   $152.77   $152.75   $152.80  
  Purchase #5 $157.39   4.316%   $164.183   $164.18   $164.20   $164.20  
  Purchase #6 $204.48   6.202%   $217.1618   $217.16   $217.15   $217.20  
  Purchase #7 $222.87   8.608%   $242.0546   $242.05   $242.05   $242.10  
  7 purchase totals = $1,231.99       $1,342.6843   $1,342.68   $1,342.65   $1,342.80