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	$177.61	6.151%	$188.5348	$188.53	$188.55	$188.50
Purchase #2	$241.27	5.615%	$254.8173	$254.82	$254.80	$254.80
Purchase #3	$111.80	12.105%	$125.3334	$125.33	$125.35	$125.30
Purchase #4	$28.73	3.717%	$29.7979	$29.80	$29.80	$29.80
Purchase #5	$88.87	13.171%	$100.5751	$100.58	$100.60	$100.60
Purchase #6	$128.82	9.655%	$141.2576	$141.26	$141.25	$141.30
Purchase #7	$41.90	12.160%	$46.995	$47.00	$47.00	$47.00
7 purchase totals =	$819.00		$887.3111	$887.32	$887.35	$887.30