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 $53.51   8.603%   $58.1135   $58.11   $58.10   $58.10  
  Purchase #2 $118.51   5.842%   $125.4334   $125.43   $125.45   $125.40  
  Purchase #3 $131.41   6.805%   $140.3525   $140.35   $140.35   $140.40  
  Purchase #4 $114.95   6.656%   $122.6011   $122.60   $122.60   $122.60  
  Purchase #5 $43.73   9.461%   $47.8673   $47.87   $47.85   $47.90  
  Purchase #6 $81.90   9.323%   $89.5355   $89.54   $89.55   $89.50  
  Purchase #7 $87.78   5.242%   $92.3814   $92.38   $92.40   $92.40  
  7 purchase totals = $631.79       $676.2847   $676.28   $676.30   $676.30