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	$84.29	4.681%	$88.2356	$88.24	$88.25	$88.20
Purchase #2	$97.39	12.826%	$109.8812	$109.88	$109.90	$109.90
Purchase #3	$105.91	10.569%	$117.1036	$117.10	$117.10	$117.10
Purchase #4	$6.89	12.615%	$7.7592	$7.76	$7.75	$7.80
Purchase #5	$48.76	5.743%	$51.5603	$51.56	$51.55	$51.60
Purchase #6	$20.85	4.720%	$21.8341	$21.83	$21.85	$21.80
Purchase #7	$166.28	4.502%	$173.7659	$173.77	$173.75	$173.80
7 purchase totals =	$530.37		$570.1399	$570.14	$570.15	$570.20