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	$81.43	13.110%	$92.1055	$92.11	$92.10	$92.10
Purchase #2	$133.76	8.707%	$145.4065	$145.41	$145.40	$145.40
Purchase #3	$226.64	12.535%	$255.0493	$255.05	$255.05	$255.00
Purchase #4	$38.59	11.125%	$42.8831	$42.88	$42.90	$42.90
Purchase #5	$180.95	13.673%	$205.6913	$205.69	$205.70	$205.70
Purchase #6	$79.84	13.677%	$90.7597	$90.76	$90.75	$90.80
Purchase #7	$50.56	10.158%	$55.6959	$55.70	$55.70	$55.70
7 purchase totals =	$791.77		$887.5913	$887.60	$887.60	$887.60