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 $248.94   7.227%   $266.9309   $266.93   $266.95   $266.90  
  Purchase #2 $95.90   7.635%   $103.222   $103.22   $103.20   $103.20  
  Purchase #3 $135.74   3.540%   $140.5452   $140.55   $140.55   $140.50  
  Purchase #4 $177.69   8.589%   $192.9518   $192.95   $192.95   $193.00  
  Purchase #5 $176.69   10.851%   $195.8626   $195.86   $195.85   $195.90  
  Purchase #6 $156.64   8.226%   $169.5252   $169.53   $169.55   $169.50  
  Purchase #7 $185.49   8.744%   $201.7092   $201.71   $201.70   $201.70  
  7 purchase totals = $1,177.09       $1,270.7469   $1,270.75   $1,270.75   $1,270.70