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	$53.61	3.187%	$55.3186	$55.32	$55.30	$55.30
Purchase #2	$149.54	4.391%	$156.1063	$156.11	$156.10	$156.10
Purchase #3	$152.72	6.840%	$163.166	$163.17	$163.15	$163.20
Purchase #4	$164.81	4.120%	$171.6002	$171.60	$171.60	$171.60
Purchase #5	$116.92	8.828%	$127.2417	$127.24	$127.25	$127.20
Purchase #6	$83.85	8.778%	$91.2104	$91.21	$91.20	$91.20
Purchase #7	$157.27	10.373%	$173.5836	$173.58	$173.60	$173.60
7 purchase totals =	$878.72		$938.2268	$938.23	$938.20	$938.20