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	$42.52	3.483%	$44.001	$44.00	$44.00	$44.00
Purchase #2	$104.90	3.290%	$108.3512	$108.35	$108.35	$108.40
Purchase #3	$35.31	5.849%	$37.3753	$37.38	$37.40	$37.40
Purchase #4	$79.82	8.321%	$86.4618	$86.46	$86.45	$86.50
Purchase #5	$23.46	9.183%	$25.6143	$25.61	$25.60	$25.60
Purchase #6	$215.43	10.669%	$238.4142	$238.41	$238.40	$238.40
Purchase #7	$47.79	6.838%	$51.0579	$51.06	$51.05	$51.10
7 purchase totals =	$549.23		$591.2757	$591.27	$591.25	$591.40