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	$71.48	8.500%	$77.5558	$77.56	$77.55	$77.60
Purchase #2	$158.30	9.755%	$173.7422	$173.74	$173.75	$173.70
Purchase #3	$218.81	4.234%	$228.0744	$228.07	$228.05	$228.10
Purchase #4	$156.51	10.418%	$172.8152	$172.82	$172.80	$172.80
Purchase #5	$190.48	8.418%	$206.5146	$206.51	$206.50	$206.50
Purchase #6	$154.71	8.319%	$167.5803	$167.58	$167.60	$167.60
Purchase #7	$229.93	10.476%	$254.0175	$254.02	$254.00	$254.00
7 purchase totals =	$1,180.22		$1,280.3000	$1,280.30	$1,280.25	$1,280.30