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 $84.44   9.128%   $92.1477   $92.15   $92.15   $92.10  
  Purchase #2 $92.38   12.292%   $103.7353   $103.74   $103.75   $103.70  
  Purchase #3 $188.98   7.599%   $203.3406   $203.34   $203.35   $203.30  
  Purchase #4 $86.46   6.291%   $91.8992   $91.90   $91.90   $91.90  
  Purchase #5 $96.32   7.858%   $103.8888   $103.89   $103.90   $103.90  
  Purchase #6 $146.95   12.582%   $165.4392   $165.44   $165.45   $165.40  
  Purchase #7 $198.88   4.825%   $208.476   $208.48   $208.50   $208.50  
  7 purchase totals = $894.41       $968.9268   $968.94   $969.00   $968.80