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	$106.46	8.501%	$115.5102	$115.51	$115.50	$115.50
Purchase #2	$77.83	4.486%	$81.3215	$81.32	$81.30	$81.30
Purchase #3	$223.94	10.583%	$247.6396	$247.64	$247.65	$247.60
Purchase #4	$62.96	11.739%	$70.3509	$70.35	$70.35	$70.40
Purchase #5	$238.49	7.718%	$256.8967	$256.90	$256.90	$256.90
Purchase #6	$166.69	3.338%	$172.2541	$172.25	$172.25	$172.30
Purchase #7	$93.69	13.706%	$106.5312	$106.53	$106.55	$106.50
7 purchase totals =	$970.06		$1,050.5042	$1,050.50	$1,050.50	$1,050.50