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	$81.89	12.662%	$92.2589	$92.26	$92.25	$92.30
Purchase #2	$54.33	4.201%	$56.6124	$56.61	$56.60	$56.60
Purchase #3	$141.80	8.106%	$153.2943	$153.29	$153.30	$153.30
Purchase #4	$161.35	11.204%	$179.4277	$179.43	$179.45	$179.40
Purchase #5	$129.55	9.769%	$142.2057	$142.21	$142.20	$142.20
Purchase #6	$35.98	6.300%	$38.2467	$38.25	$38.25	$38.20
Purchase #7	$127.41	12.289%	$143.0674	$143.07	$143.05	$143.10
7 purchase totals =	$732.31		$805.1131	$805.12	$805.10	$805.10