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	$24.80	13.379%	$28.118	$28.12	$28.10	$28.10
Purchase #2	$158.76	8.784%	$172.7055	$172.71	$172.70	$172.70
Purchase #3	$156.58	3.636%	$162.2732	$162.27	$162.25	$162.30
Purchase #4	$53.64	11.789%	$59.9636	$59.96	$59.95	$60.00
Purchase #5	$59.64	6.666%	$63.6156	$63.62	$63.60	$63.60
Purchase #6	$5.95	6.408%	$6.3313	$6.33	$6.35	$6.30
Purchase #7	$88.89	8.578%	$96.515	$96.52	$96.50	$96.50
7 purchase totals =	$548.26		$589.5222	$589.53	$589.45	$589.50