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	$75.41	10.720%	$83.494	$83.49	$83.50	$83.50
Purchase #2	$111.74	3.660%	$115.8297	$115.83	$115.85	$115.80
Purchase #3	$90.30	9.658%	$99.0212	$99.02	$99.00	$99.00
Purchase #4	$158.36	10.326%	$174.7123	$174.71	$174.70	$174.70
Purchase #5	$223.28	3.335%	$230.7264	$230.73	$230.75	$230.70
Purchase #6	$11.78	9.447%	$12.8929	$12.89	$12.90	$12.90
Purchase #7	$146.59	12.131%	$164.3728	$164.37	$164.35	$164.40
7 purchase totals =	$817.46		$881.0493	$881.04	$881.05	$881.00