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	$5.72	7.813%	$6.1669	$6.17	$6.15	$6.20
Purchase #2	$198.39	6.324%	$210.9362	$210.94	$210.95	$210.90
Purchase #3	$74.41	11.201%	$82.7447	$82.74	$82.75	$82.70
Purchase #4	$134.89	3.341%	$139.3967	$139.40	$139.40	$139.40
Purchase #5	$160.25	3.307%	$165.5495	$165.55	$165.55	$165.50
Purchase #6	$53.65	4.182%	$55.8936	$55.89	$55.90	$55.90
Purchase #7	$130.64	5.542%	$137.8801	$137.88	$137.90	$137.90
7 purchase totals =	$757.95		$798.5677	$798.57	$798.60	$798.50