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 $179.26   9.857%   $196.9297   $196.93   $196.95   $196.90  
  Purchase #2 $165.72   12.311%   $186.1218   $186.12   $186.10   $186.10  
  Purchase #3 $45.86   7.395%   $49.2513   $49.25   $49.25   $49.30  
  Purchase #4 $23.80   10.826%   $26.3766   $26.38   $26.40   $26.40  
  Purchase #5 $175.89   4.154%   $183.1965   $183.20   $183.20   $183.20  
  Purchase #6 $242.92   6.620%   $259.0013   $259.00   $259.00   $259.00  
  Purchase #7 $162.33   5.344%   $171.0049   $171.00   $171.00   $171.00  
  7 purchase totals = $995.78       $1,071.8821   $1,071.88   $1,071.90   $1,071.90