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 $104.85   3.396%   $108.4107   $108.41   $108.40   $108.40  
  Purchase #2 $12.86   9.185%   $14.0412   $14.04   $14.05   $14.00  
  Purchase #3 $112.48   3.543%   $116.4652   $116.47   $116.45   $116.50  
  Purchase #4 $241.94   8.834%   $263.313   $263.31   $263.30   $263.30  
  Purchase #5 $66.71   5.724%   $70.5285   $70.53   $70.55   $70.50  
  Purchase #6 $208.90   11.455%   $232.8295   $232.83   $232.85   $232.80  
  Purchase #7 $153.61   8.432%   $166.5624   $166.56   $166.55   $166.60  
  7 purchase totals = $901.35       $972.1505   $972.15   $972.15   $972.10