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	$126.73	13.529%	$143.8753	$143.88	$143.90	$143.90
Purchase #2	$170.72	8.102%	$184.5517	$184.55	$184.55	$184.60
Purchase #3	$31.39	11.327%	$34.9455	$34.95	$34.95	$34.90
Purchase #4	$34.44	10.749%	$38.142	$38.14	$38.15	$38.10
Purchase #5	$179.33	3.229%	$185.1206	$185.12	$185.10	$185.10
Purchase #6	$88.79	12.247%	$99.6641	$99.66	$99.65	$99.70
Purchase #7	$156.94	9.717%	$172.1899	$172.19	$172.20	$172.20
7 purchase totals =	$788.34		$858.4891	$858.49	$858.50	$858.50