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 $29.86   12.547%   $33.6065   $33.61   $33.60   $33.60  
  Purchase #2 $133.94   6.611%   $142.7948   $142.79   $142.80   $142.80  
  Purchase #3 $62.61   7.736%   $67.4535   $67.45   $67.45   $67.50  
  Purchase #4 $230.40   9.703%   $252.7557   $252.76   $252.75   $252.80  
  Purchase #5 $166.48   4.131%   $173.3573   $173.36   $173.35   $173.40  
  Purchase #6 $67.74   9.838%   $74.4043   $74.40   $74.40   $74.40  
  Purchase #7 $238.38   4.522%   $249.1595   $249.16   $249.15   $249.20  
  7 purchase totals = $929.41       $993.5316   $993.53   $993.50   $993.70