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 $211.82   6.835%   $226.2979   $226.30   $226.30   $226.30  
  Purchase #2 $67.62   12.570%   $76.1198   $76.12   $76.10   $76.10  
  Purchase #3 $79.47   9.842%   $87.2914   $87.29   $87.30   $87.30  
  Purchase #4 $183.54   13.836%   $208.9346   $208.93   $208.95   $208.90  
  Purchase #5 $98.56   6.665%   $105.129   $105.13   $105.15   $105.10  
  Purchase #6 $135.34   5.515%   $142.804   $142.80   $142.80   $142.80  
  Purchase #7 $105.28   12.296%   $118.2252   $118.23   $118.25   $118.20  
  7 purchase totals = $881.63       $964.8019   $964.80   $964.85   $964.70