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	$135.55	7.297%	$145.4411	$145.44	$145.45	$145.40
Purchase #2	$169.76	6.663%	$181.0711	$181.07	$181.05	$181.10
Purchase #3	$69.61	12.615%	$78.3913	$78.39	$78.40	$78.40
Purchase #4	$235.60	10.588%	$260.5453	$260.55	$260.55	$260.50
Purchase #5	$69.43	12.454%	$78.0768	$78.08	$78.10	$78.10
Purchase #6	$23.79	4.323%	$24.8184	$24.82	$24.80	$24.80
Purchase #7	$155.73	9.111%	$169.9186	$169.92	$169.90	$169.90
7 purchase totals =	$859.47		$938.2626	$938.27	$938.25	$938.20