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	$15.50	10.387%	$17.11	$17.11	$17.10	$17.10
Purchase #2	$99.97	5.563%	$105.5313	$105.53	$105.55	$105.50
Purchase #3	$19.28	7.543%	$20.7343	$20.73	$20.75	$20.70
Purchase #4	$145.73	11.486%	$162.4685	$162.47	$162.45	$162.50
Purchase #5	$96.51	12.438%	$108.5139	$108.51	$108.50	$108.50
Purchase #6	$65.67	3.173%	$67.7537	$67.75	$67.75	$67.80
Purchase #7	$173.25	9.818%	$190.2597	$190.26	$190.25	$190.30
7 purchase totals =	$615.91		$672.3714	$672.36	$672.35	$672.40