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	$129.99	10.225%	$143.2815	$143.28	$143.30	$143.30
Purchase #2	$156.70	6.442%	$166.7946	$166.79	$166.80	$166.80
Purchase #3	$64.61	12.250%	$72.5247	$72.52	$72.50	$72.50
Purchase #4	$147.45	3.419%	$152.4913	$152.49	$152.50	$152.50
Purchase #5	$41.53	4.269%	$43.3029	$43.30	$43.30	$43.30
Purchase #6	$49.60	7.829%	$53.4832	$53.48	$53.50	$53.50
Purchase #7	$56.32	4.246%	$58.7113	$58.71	$58.70	$58.70
7 purchase totals =	$646.20		$690.5895	$690.57	$690.60	$690.60