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	$30.64	13.506%	$34.7782	$34.78	$34.80	$34.80
Purchase #2	$173.94	10.137%	$191.5723	$191.57	$191.55	$191.60
Purchase #3	$166.59	3.315%	$172.1125	$172.11	$172.10	$172.10
Purchase #4	$54.52	4.837%	$57.1571	$57.16	$57.15	$57.20
Purchase #5	$89.55	7.161%	$95.9627	$95.96	$95.95	$96.00
Purchase #6	$192.27	3.417%	$198.8399	$198.84	$198.85	$198.80
Purchase #7	$123.39	11.243%	$137.2627	$137.26	$137.25	$137.30
7 purchase totals =	$830.90		$887.6854	$887.68	$887.65	$887.80