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 $93.38   3.618%   $96.7585   $96.76   $96.75   $96.80  
  Purchase #2 $72.51   13.142%   $82.0393   $82.04   $82.05   $82.00  
  Purchase #3 $167.64   10.490%   $185.2254   $185.23   $185.25   $185.20  
  Purchase #4 $55.59   13.802%   $63.2625   $63.26   $63.25   $63.30  
  Purchase #5 $228.77   4.611%   $239.3186   $239.32   $239.30   $239.30  
  Purchase #6 $123.48   6.573%   $131.5963   $131.60   $131.60   $131.60  
  Purchase #7 $175.26   11.278%   $195.0258   $195.03   $195.05   $195.00  
  7 purchase totals = $916.63       $993.2264   $993.24   $993.25   $993.20