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 $87.95   7.521%   $94.5647   $94.56   $94.55   $94.60  
  Purchase #2 $193.95   11.480%   $216.2155   $216.22   $216.20   $216.20  
  Purchase #3 $45.61   13.211%   $51.6355   $51.64   $51.65   $51.60  
  Purchase #4 $176.35   8.607%   $191.5284   $191.53   $191.55   $191.50  
  Purchase #5 $104.50   9.473%   $114.3993   $114.40   $114.40   $114.40  
  Purchase #6 $178.99   3.385%   $185.0488   $185.05   $185.05   $185.00  
  Purchase #7 $44.77   4.315%   $46.7018   $46.70   $46.70   $46.70  
  7 purchase totals = $832.12       $900.0940   $900.10   $900.10   $900.00