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 $229.79   12.508%   $258.5321   $258.53   $258.55   $258.50  
  Purchase #2 $23.25   12.748%   $26.2139   $26.21   $26.20   $26.20  
  Purchase #3 $31.72   12.103%   $35.5591   $35.56   $35.55   $35.60  
  Purchase #4 $67.57   5.599%   $71.3532   $71.35   $71.35   $71.40  
  Purchase #5 $180.69   7.456%   $194.1622   $194.16   $194.15   $194.20  
  Purchase #6 $164.50   6.182%   $174.6694   $174.67   $174.65   $174.70  
  Purchase #7 $208.37   6.494%   $221.9015   $221.90   $221.90   $221.90  
  7 purchase totals = $905.89       $982.3914   $982.38   $982.35   $982.50