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 $159.25   10.537%   $176.0302   $176.03   $176.05   $176.00  
  Purchase #2 $94.46   9.605%   $103.5329   $103.53   $103.55   $103.50  
  Purchase #3 $124.31   4.725%   $130.1836   $130.18   $130.20   $130.20  
  Purchase #4 $81.59   10.237%   $89.9424   $89.94   $89.95   $89.90  
  Purchase #5 $75.81   11.522%   $84.5448   $84.54   $84.55   $84.50  
  Purchase #6 $211.66   13.122%   $239.434   $239.43   $239.45   $239.40  
  Purchase #7 $166.40   11.166%   $184.9802   $184.98   $185.00   $185.00  
  7 purchase totals = $913.48       $1,008.6481   $1,008.63   $1,008.75   $1,008.50