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 $151.32   9.679%   $165.9663   $165.97   $165.95   $166.00  
  Purchase #2 $23.51   7.445%   $25.2603   $25.26   $25.25   $25.30  
  Purchase #3 $112.93   5.629%   $119.2868   $119.29   $119.30   $119.30  
  Purchase #4 $114.60   4.662%   $119.9427   $119.94   $119.95   $119.90  
  Purchase #5 $244.92   8.237%   $265.0941   $265.09   $265.10   $265.10  
  Purchase #6 $61.59   6.769%   $65.759   $65.76   $65.75   $65.80  
  Purchase #7 $239.42   3.196%   $247.0719   $247.07   $247.05   $247.10  
  7 purchase totals = $948.29       $1,008.3811   $1,008.38   $1,008.35   $1,008.50