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	$127.32	13.663%	$144.7157	$144.72	$144.70	$144.70
Purchase #2	$77.40	4.221%	$80.6671	$80.67	$80.65	$80.70
Purchase #3	$126.56	13.769%	$143.986	$143.99	$144.00	$144.00
Purchase #4	$72.84	10.626%	$80.58	$80.58	$80.60	$80.60
Purchase #5	$90.80	6.234%	$96.4605	$96.46	$96.45	$96.50
Purchase #6	$211.85	8.351%	$229.5416	$229.54	$229.55	$229.50
Purchase #7	$49.78	10.315%	$54.9148	$54.91	$54.90	$54.90
7 purchase totals =	$756.55		$830.8657	$830.87	$830.85	$830.90