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 $210.36   5.109%   $221.1073   $221.11   $221.10   $221.10  
  Purchase #2 $200.46   4.504%   $209.4887   $209.49   $209.50   $209.50  
  Purchase #3 $42.54   12.152%   $47.7095   $47.71   $47.70   $47.70  
  Purchase #4 $127.76   7.518%   $137.365   $137.37   $137.35   $137.40  
  Purchase #5 $197.87   5.258%   $208.274   $208.27   $208.25   $208.30  
  Purchase #6 $167.68   9.227%   $183.1518   $183.15   $183.15   $183.20  
  Purchase #7 $23.57   12.422%   $26.4979   $26.50   $26.50   $26.50  
  7 purchase totals = $970.24       $1,033.5942   $1,033.60   $1,033.55   $1,033.70