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	$79.85	11.263%	$88.8435	$88.84	$88.85	$88.80
Purchase #2	$122.71	4.257%	$127.9338	$127.93	$127.95	$127.90
Purchase #3	$47.28	8.545%	$51.3201	$51.32	$51.30	$51.30
Purchase #4	$64.58	3.486%	$66.8313	$66.83	$66.85	$66.80
Purchase #5	$170.38	12.371%	$191.4577	$191.46	$191.45	$191.50
Purchase #6	$85.77	7.288%	$92.0209	$92.02	$92.00	$92.00
Purchase #7	$12.98	4.792%	$13.602	$13.60	$13.60	$13.60
7 purchase totals =	$583.55		$632.0093	$632.00	$632.00	$631.90