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	$134.73	12.232%	$151.2102	$151.21	$151.20	$151.20
Purchase #2	$33.51	11.567%	$37.3861	$37.39	$37.40	$37.40
Purchase #3	$128.65	11.517%	$143.4666	$143.47	$143.45	$143.50
Purchase #4	$144.54	11.381%	$160.9901	$160.99	$161.00	$161.00
Purchase #5	$24.63	13.145%	$27.8676	$27.87	$27.85	$27.90
Purchase #6	$132.50	9.714%	$145.3711	$145.37	$145.35	$145.40
Purchase #7	$101.55	7.791%	$109.4618	$109.46	$109.45	$109.50
7 purchase totals =	$700.11		$775.7535	$775.76	$775.70	$775.90