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 $188.66   10.606%   $208.6693   $208.67   $208.65   $208.70  
  Purchase #2 $166.58   5.329%   $175.457   $175.46   $175.45   $175.50  
  Purchase #3 $48.27   8.864%   $52.5487   $52.55   $52.55   $52.50  
  Purchase #4 $87.61   9.710%   $96.1169   $96.12   $96.10   $96.10  
  Purchase #5 $166.67   10.544%   $184.2437   $184.24   $184.25   $184.20  
  Purchase #6 $122.25   3.724%   $126.8026   $126.80   $126.80   $126.80  
  Purchase #7 $63.47   5.502%   $66.9621   $66.96   $66.95   $67.00  
  7 purchase totals = $843.51       $910.8003   $910.80   $910.75   $910.80