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	$38.71	8.718%	$42.0847	$42.08	$42.10	$42.10
Purchase #2	$137.73	10.265%	$151.868	$151.87	$151.85	$151.90
Purchase #3	$171.80	7.476%	$184.6438	$184.64	$184.65	$184.60
Purchase #4	$137.44	10.771%	$152.2437	$152.24	$152.25	$152.20
Purchase #5	$160.45	7.272%	$172.1179	$172.12	$172.10	$172.10
Purchase #6	$53.74	10.312%	$59.2817	$59.28	$59.30	$59.30
Purchase #7	$166.76	3.408%	$172.4432	$172.44	$172.45	$172.40
7 purchase totals =	$866.63		$934.6830	$934.67	$934.70	$934.60