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	$189.38	7.577%	$203.7293	$203.73	$203.75	$203.70
Purchase #2	$94.49	13.445%	$107.1942	$107.19	$107.20	$107.20
Purchase #3	$142.57	13.293%	$161.5218	$161.52	$161.50	$161.50
Purchase #4	$116.54	12.539%	$131.153	$131.15	$131.15	$131.20
Purchase #5	$154.89	11.603%	$172.8619	$172.86	$172.85	$172.90
Purchase #6	$211.50	7.854%	$228.1112	$228.11	$228.10	$228.10
Purchase #7	$13.59	10.630%	$15.0346	$15.03	$15.05	$15.00
7 purchase totals =	$922.96		$1,019.6060	$1,019.59	$1,019.60	$1,019.60