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 $95.48   3.487%   $98.8094   $98.81   $98.80   $98.80  
  Purchase #2 $182.33   8.407%   $197.6585   $197.66   $197.65   $197.70  
  Purchase #3 $84.66   7.186%   $90.7437   $90.74   $90.75   $90.70  
  Purchase #4 $148.82   4.325%   $155.2565   $155.26   $155.25   $155.30  
  Purchase #5 $35.77   13.749%   $40.688   $40.69   $40.70   $40.70  
  Purchase #6 $230.51   7.754%   $248.3837   $248.38   $248.40   $248.40  
  Purchase #7 $212.27   11.784%   $237.2839   $237.28   $237.30   $237.30  
  7 purchase totals = $989.84       $1,068.8237   $1,068.82   $1,068.85   $1,068.90