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 $144.25   12.579%   $162.3952   $162.40   $162.40   $162.40  
  Purchase #2 $42.98   11.127%   $47.7624   $47.76   $47.75   $47.80  
  Purchase #3 $205.33   4.452%   $214.4713   $214.47   $214.45   $214.50  
  Purchase #4 $162.74   8.553%   $176.6592   $176.66   $176.65   $176.70  
  Purchase #5 $142.68   13.470%   $161.899   $161.90   $161.90   $161.90  
  Purchase #6 $143.30   5.612%   $151.342   $151.34   $151.35   $151.30  
  Purchase #7 $233.38   9.280%   $255.0377   $255.04   $255.05   $255.00  
  7 purchase totals = $1,074.66       $1,169.5668   $1,169.57   $1,169.55   $1,169.60