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	$146.84	13.390%	$166.5019	$166.50	$166.50	$166.50
Purchase #2	$210.78	10.743%	$233.4241	$233.42	$233.40	$233.40
Purchase #3	$60.98	10.773%	$67.5494	$67.55	$67.55	$67.50
Purchase #4	$93.64	3.354%	$96.7807	$96.78	$96.80	$96.80
Purchase #5	$244.75	4.512%	$255.7931	$255.79	$255.80	$255.80
Purchase #6	$146.58	9.784%	$160.9214	$160.92	$160.90	$160.90
Purchase #7	$241.97	11.551%	$269.92	$269.92	$269.90	$269.90
7 purchase totals =	$1,145.54		$1,250.8906	$1,250.88	$1,250.85	$1,250.80