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	$153.48	5.236%	$161.5162	$161.52	$161.50	$161.50
Purchase #2	$53.83	12.502%	$60.5598	$60.56	$60.55	$60.60
Purchase #3	$54.47	12.444%	$61.2482	$61.25	$61.25	$61.20
Purchase #4	$18.71	12.148%	$20.9829	$20.98	$21.00	$21.00
Purchase #5	$127.28	12.484%	$143.1696	$143.17	$143.15	$143.20
Purchase #6	$111.84	9.522%	$122.4894	$122.49	$122.50	$122.50
Purchase #7	$43.97	3.131%	$45.3467	$45.35	$45.35	$45.30
7 purchase totals =	$563.58		$615.3128	$615.32	$615.30	$615.30