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	$165.98	3.209%	$171.3063	$171.31	$171.30	$171.30
Purchase #2	$247.76	3.233%	$255.7701	$255.77	$255.75	$255.80
Purchase #3	$144.32	10.701%	$159.7637	$159.76	$159.75	$159.80
Purchase #4	$11.78	12.420%	$13.2431	$13.24	$13.25	$13.20
Purchase #5	$52.51	7.560%	$56.4798	$56.48	$56.50	$56.50
Purchase #6	$74.82	4.602%	$78.2632	$78.26	$78.25	$78.30
Purchase #7	$178.78	3.380%	$184.8228	$184.82	$184.80	$184.80
7 purchase totals =	$875.95		$919.6490	$919.64	$919.60	$919.70