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 $151.61   9.330%   $165.7552   $165.76   $165.75   $165.80  
  Purchase #2 $238.41   8.731%   $259.2256   $259.23   $259.25   $259.20  
  Purchase #3 $185.55   5.411%   $195.5901   $195.59   $195.60   $195.60  
  Purchase #4 $217.62   7.127%   $233.1298   $233.13   $233.15   $233.10  
  Purchase #5 $129.92   9.299%   $142.0013   $142.00   $142.00   $142.00  
  Purchase #6 $245.38   5.620%   $259.1704   $259.17   $259.15   $259.20  
  Purchase #7 $227.26   13.176%   $257.2038   $257.20   $257.20   $257.20  
  7 purchase totals = $1,395.75       $1,512.0762   $1,512.08   $1,512.10   $1,512.10