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	$118.87	10.585%	$131.4524	$131.45	$131.45	$131.50
Purchase #2	$173.99	5.395%	$183.3768	$183.38	$183.40	$183.40
Purchase #3	$147.36	3.251%	$152.1507	$152.15	$152.15	$152.20
Purchase #4	$86.30	7.695%	$92.9408	$92.94	$92.95	$92.90
Purchase #5	$165.32	4.302%	$172.4321	$172.43	$172.45	$172.40
Purchase #6	$101.88	10.641%	$112.7211	$112.72	$112.70	$112.70
Purchase #7	$113.50	12.777%	$128.0019	$128.00	$128.00	$128.00
7 purchase totals =	$907.22		$973.0758	$973.07	$973.10	$973.10