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 $198.94   4.696%   $208.2822   $208.28   $208.30   $208.30  
  Purchase #2 $110.72   13.473%   $125.6373   $125.64   $125.65   $125.60  
  Purchase #3 $144.75   10.462%   $159.8937   $159.89   $159.90   $159.90  
  Purchase #4 $156.46   8.315%   $169.4696   $169.47   $169.45   $169.50  
  Purchase #5 $13.25   4.862%   $13.8942   $13.89   $13.90   $13.90  
  Purchase #6 $206.61   5.356%   $217.676   $217.68   $217.70   $217.70  
  Purchase #7 $168.88   3.526%   $174.8347   $174.83   $174.85   $174.80  
  7 purchase totals = $999.61       $1,069.6877   $1,069.68   $1,069.75   $1,069.70