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 $69.91   4.801%   $73.2664   $73.27   $73.25   $73.30  
  Purchase #2 $88.76   3.190%   $91.5914   $91.59   $91.60   $91.60  
  Purchase #3 $224.27   10.493%   $247.8027   $247.80   $247.80   $247.80  
  Purchase #4 $41.61   9.810%   $45.6919   $45.69   $45.70   $45.70  
  Purchase #5 $118.38   6.854%   $126.4938   $126.49   $126.50   $126.50  
  Purchase #6 $167.71   6.205%   $178.1164   $178.12   $178.10   $178.10  
  Purchase #7 $91.38   6.845%   $97.635   $97.64   $97.65   $97.60  
  7 purchase totals = $802.02       $860.5976   $860.60   $860.60   $860.60