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	$102.97	3.247%	$106.3134	$106.31	$106.30	$106.30
Purchase #2	$74.79	10.485%	$82.6317	$82.63	$82.65	$82.60
Purchase #3	$123.69	5.485%	$130.4744	$130.47	$130.45	$130.50
Purchase #4	$219.83	4.236%	$229.142	$229.14	$229.15	$229.10
Purchase #5	$52.75	7.585%	$56.7511	$56.75	$56.75	$56.80
Purchase #6	$46.83	12.654%	$52.7559	$52.76	$52.75	$52.80
Purchase #7	$129.95	9.584%	$142.4044	$142.40	$142.40	$142.40
7 purchase totals =	$750.81		$800.4729	$800.46	$800.45	$800.50