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	$239.89	12.529%	$269.9458	$269.95	$269.95	$269.90
Purchase #2	$140.82	9.530%	$154.2401	$154.24	$154.25	$154.20
Purchase #3	$43.93	3.442%	$45.4421	$45.44	$45.45	$45.40
Purchase #4	$99.39	6.631%	$105.9806	$105.98	$106.00	$106.00
Purchase #5	$97.31	9.534%	$106.5875	$106.59	$106.60	$106.60
Purchase #6	$134.69	6.780%	$143.822	$143.82	$143.80	$143.80
Purchase #7	$19.73	3.575%	$20.4353	$20.44	$20.45	$20.40
7 purchase totals =	$775.76		$846.4534	$846.46	$846.50	$846.30