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 $79.41   8.241%   $85.9542   $85.95   $85.95   $86.00  
  Purchase #2 $220.57   9.333%   $241.1558   $241.16   $241.15   $241.20  
  Purchase #3 $59.30   3.722%   $61.5071   $61.51   $61.50   $61.50  
  Purchase #4 $36.87   8.865%   $40.1385   $40.14   $40.15   $40.10  
  Purchase #5 $125.49   5.487%   $132.3756   $132.38   $132.40   $132.40  
  Purchase #6 $158.86   10.247%   $175.1384   $175.14   $175.15   $175.10  
  Purchase #7 $208.97   10.722%   $231.3758   $231.38   $231.40   $231.40  
  7 purchase totals = $889.47       $967.6454   $967.66   $967.70   $967.70