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	$196.61	6.574%	$209.5351	$209.54	$209.55	$209.50
Purchase #2	$46.27	10.175%	$50.978	$50.98	$51.00	$51.00
Purchase #3	$48.55	3.430%	$50.2153	$50.22	$50.20	$50.20
Purchase #4	$56.64	4.847%	$59.3853	$59.39	$59.40	$59.40
Purchase #5	$133.46	7.748%	$143.8005	$143.80	$143.80	$143.80
Purchase #6	$38.84	3.292%	$40.1186	$40.12	$40.10	$40.10
Purchase #7	$34.76	13.728%	$39.5319	$39.53	$39.55	$39.50
7 purchase totals =	$555.13		$593.5647	$593.58	$593.60	$593.50