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	$73.41	6.509%	$78.1883	$78.19	$78.20	$78.20
Purchase #2	$88.49	4.578%	$92.5411	$92.54	$92.55	$92.50
Purchase #3	$142.64	11.191%	$158.6028	$158.60	$158.60	$158.60
Purchase #4	$22.80	13.735%	$25.9316	$25.93	$25.95	$25.90
Purchase #5	$90.94	9.748%	$99.8048	$99.80	$99.80	$99.80
Purchase #6	$167.37	4.462%	$174.838	$174.84	$174.85	$174.80
Purchase #7	$222.35	3.219%	$229.5074	$229.51	$229.50	$229.50
7 purchase totals =	$808.00		$859.4140	$859.41	$859.45	$859.30