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	$243.82	13.709%	$277.2453	$277.25	$277.25	$277.20
Purchase #2	$89.66	11.137%	$99.6454	$99.65	$99.65	$99.60
Purchase #3	$110.49	7.728%	$119.0287	$119.03	$119.05	$119.00
Purchase #4	$20.60	8.406%	$22.3316	$22.33	$22.35	$22.30
Purchase #5	$51.25	6.589%	$54.6269	$54.63	$54.65	$54.60
Purchase #6	$11.75	11.297%	$13.0774	$13.08	$13.10	$13.10
Purchase #7	$53.37	11.583%	$59.5518	$59.55	$59.55	$59.60
7 purchase totals =	$580.94		$645.5071	$645.52	$645.60	$645.40