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	$214.43	7.711%	$230.9647	$230.96	$230.95	$231.00
Purchase #2	$180.31	9.444%	$197.3385	$197.34	$197.35	$197.30
Purchase #3	$165.92	5.483%	$175.0174	$175.02	$175.00	$175.00
Purchase #4	$7.48	3.487%	$7.7408	$7.74	$7.75	$7.70
Purchase #5	$120.89	6.600%	$128.8687	$128.87	$128.85	$128.90
Purchase #6	$106.61	4.229%	$111.1185	$111.12	$111.10	$111.10
Purchase #7	$117.38	11.724%	$131.1416	$131.14	$131.15	$131.10
7 purchase totals =	$913.02		$982.1902	$982.19	$982.15	$982.10