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 $232.99   5.553%   $245.9279   $245.93   $245.95   $245.90  
  Purchase #2 $30.93   10.227%   $34.0932   $34.09   $34.10   $34.10  
  Purchase #3 $133.32   7.466%   $143.2737   $143.27   $143.25   $143.30  
  Purchase #4 $126.58   8.407%   $137.2216   $137.22   $137.20   $137.20  
  Purchase #5 $124.96   5.157%   $131.4042   $131.40   $131.40   $131.40  
  Purchase #6 $125.70   8.376%   $136.2286   $136.23   $136.25   $136.20  
  Purchase #7 $112.43   3.743%   $116.6383   $116.64   $116.65   $116.60  
  7 purchase totals = $886.91       $944.7875   $944.78   $944.80   $944.70