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 $69.55   6.687%   $74.2008   $74.20   $74.20   $74.20  
  Purchase #2 $93.31   4.235%   $97.2617   $97.26   $97.25   $97.30  
  Purchase #3 $14.53   7.838%   $15.6689   $15.67   $15.65   $15.70  
  Purchase #4 $60.57   6.711%   $64.6349   $64.63   $64.65   $64.60  
  Purchase #5 $183.84   6.669%   $196.1003   $196.10   $196.10   $196.10  
  Purchase #6 $225.32   6.299%   $239.5129   $239.51   $239.50   $239.50  
  Purchase #7 $158.25   6.214%   $168.0837   $168.08   $168.10   $168.10  
  7 purchase totals = $805.37       $855.4632   $855.45   $855.45   $855.50