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 $179.30   8.177%   $193.9614   $193.96   $193.95   $194.00  
  Purchase #2 $230.97   3.861%   $239.8878   $239.89   $239.90   $239.90  
  Purchase #3 $242.58   4.451%   $253.3772   $253.38   $253.40   $253.40  
  Purchase #4 $247.39   7.225%   $265.2639   $265.26   $265.25   $265.30  
  Purchase #5 $101.99   9.141%   $111.3129   $111.31   $111.30   $111.30  
  Purchase #6 $146.35   11.304%   $162.8934   $162.89   $162.90   $162.90  
  Purchase #7 $24.30   10.711%   $26.9028   $26.90   $26.90   $26.90  
  7 purchase totals = $1,172.88       $1,253.5994   $1,253.59   $1,253.60   $1,253.70