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 $61.52   6.556%   $65.5533   $65.55   $65.55   $65.60  
  Purchase #2 $242.53   10.336%   $267.5979   $267.60   $267.60   $267.60  
  Purchase #3 $128.90   10.395%   $142.2992   $142.30   $142.30   $142.30  
  Purchase #4 $64.64   13.139%   $73.133   $73.13   $73.15   $73.10  
  Purchase #5 $19.58   9.688%   $21.4769   $21.48   $21.50   $21.50  
  Purchase #6 $241.90   8.422%   $262.2728   $262.27   $262.25   $262.30  
  Purchase #7 $73.26   4.265%   $76.3845   $76.38   $76.40   $76.40  
  7 purchase totals = $832.33       $908.7176   $908.71   $908.75   $908.80