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	$28.38	6.871%	$30.33	$30.33	$30.35	$30.30
Purchase #2	$85.48	13.178%	$96.7446	$96.74	$96.75	$96.70
Purchase #3	$65.76	8.482%	$71.3378	$71.34	$71.35	$71.30
Purchase #4	$165.65	4.521%	$173.139	$173.14	$173.15	$173.10
Purchase #5	$152.43	13.729%	$173.3571	$173.36	$173.35	$173.40
Purchase #6	$81.39	10.764%	$90.1508	$90.15	$90.15	$90.20
Purchase #7	$96.65	6.723%	$103.1478	$103.15	$103.15	$103.10
7 purchase totals =	$675.74		$738.2071	$738.21	$738.25	$738.10