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 $23.82   10.583%   $26.3409   $26.34   $26.35   $26.30  
  Purchase #2 $74.71   12.387%   $83.9643   $83.96   $83.95   $84.00  
  Purchase #3 $248.48   6.198%   $263.8808   $263.88   $263.90   $263.90  
  Purchase #4 $181.47   6.743%   $193.7065   $193.71   $193.70   $193.70  
  Purchase #5 $62.32   11.203%   $69.3017   $69.30   $69.30   $69.30  
  Purchase #6 $67.84   11.391%   $75.5677   $75.57   $75.55   $75.60  
  Purchase #7 $214.78   3.528%   $222.3574   $222.36   $222.35   $222.40  
  7 purchase totals = $873.42       $935.1193   $935.12   $935.10   $935.20