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	$136.92	9.419%	$149.8165	$149.82	$149.80	$149.80
Purchase #2	$93.85	10.263%	$103.4818	$103.48	$103.50	$103.50
Purchase #3	$148.83	12.655%	$167.6644	$167.66	$167.65	$167.70
Purchase #4	$68.93	13.719%	$78.3865	$78.39	$78.40	$78.40
Purchase #5	$148.77	3.807%	$154.4337	$154.43	$154.45	$154.40
Purchase #6	$23.74	7.478%	$25.5153	$25.52	$25.50	$25.50
Purchase #7	$47.49	5.622%	$50.1599	$50.16	$50.15	$50.20
7 purchase totals =	$668.53		$729.4581	$729.46	$729.45	$729.50