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	$216.68	3.297%	$223.8239	$223.82	$223.80	$223.80
Purchase #2	$40.70	9.295%	$44.4831	$44.48	$44.50	$44.50
Purchase #3	$144.51	5.220%	$152.0534	$152.05	$152.05	$152.10
Purchase #4	$44.96	4.350%	$46.9158	$46.92	$46.90	$46.90
Purchase #5	$23.75	8.345%	$25.7319	$25.73	$25.75	$25.70
Purchase #6	$93.50	10.327%	$103.1557	$103.16	$103.15	$103.20
Purchase #7	$90.86	10.483%	$100.3849	$100.38	$100.40	$100.40
7 purchase totals =	$654.96		$696.5487	$696.54	$696.55	$696.60