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 $24.68   10.229%   $27.2045   $27.20   $27.20   $27.20  
  Purchase #2 $167.74   4.241%   $174.8539   $174.85   $174.85   $174.90  
  Purchase #3 $51.43   10.289%   $56.7216   $56.72   $56.70   $56.70  
  Purchase #4 $216.58   7.847%   $233.575   $233.58   $233.60   $233.60  
  Purchase #5 $171.30   6.784%   $182.921   $182.92   $182.90   $182.90  
  Purchase #6 $38.90   8.359%   $42.1517   $42.15   $42.15   $42.20  
  Purchase #7 $108.43   7.176%   $116.2109   $116.21   $116.20   $116.20  
  7 purchase totals = $779.06       $833.6386   $833.63   $833.60   $833.70