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 $17.86   9.247%   $19.5115   $19.51   $19.50   $19.50  
  Purchase #2 $188.64   10.740%   $208.8999   $208.90   $208.90   $208.90  
  Purchase #3 $230.46   4.447%   $240.7086   $240.71   $240.70   $240.70  
  Purchase #4 $248.54   9.581%   $272.3526   $272.35   $272.35   $272.40  
  Purchase #5 $165.86   11.676%   $185.2258   $185.23   $185.25   $185.20  
  Purchase #6 $48.37   4.509%   $50.551   $50.55   $50.55   $50.60  
  Purchase #7 $87.26   10.466%   $96.3926   $96.39   $96.40   $96.40  
  7 purchase totals = $986.99       $1,073.6420   $1,073.64   $1,073.65   $1,073.70