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 $207.60   3.655%   $215.1878   $215.19   $215.20   $215.20  
  Purchase #2 $18.87   13.164%   $21.354   $21.35   $21.35   $21.40  
  Purchase #3 $217.66   5.437%   $229.4942   $229.49   $229.50   $229.50  
  Purchase #4 $61.85   8.628%   $67.1864   $67.19   $67.20   $67.20  
  Purchase #5 $230.92   11.318%   $257.0555   $257.06   $257.05   $257.10  
  Purchase #6 $22.75   11.533%   $25.3738   $25.37   $25.35   $25.40  
  Purchase #7 $239.42   5.480%   $252.5402   $252.54   $252.55   $252.50  
  7 purchase totals = $999.07       $1,068.1919   $1,068.19   $1,068.20   $1,068.30