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	$52.82	13.122%	$59.751	$59.75	$59.75	$59.80
Purchase #2	$222.84	8.698%	$242.2226	$242.22	$242.20	$242.20
Purchase #3	$230.43	5.174%	$242.3524	$242.35	$242.35	$242.40
Purchase #4	$110.82	11.712%	$123.7992	$123.80	$123.80	$123.80
Purchase #5	$177.34	13.730%	$201.6888	$201.69	$201.70	$201.70
Purchase #6	$11.88	5.280%	$12.5073	$12.51	$12.50	$12.50
Purchase #7	$250.78	3.729%	$260.1316	$260.13	$260.15	$260.10
7 purchase totals =	$1,056.91		$1,142.4529	$1,142.45	$1,142.45	$1,142.50