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	$159.46	13.233%	$180.5613	$180.56	$180.55	$180.60
Purchase #2	$174.89	13.309%	$198.1661	$198.17	$198.15	$198.20
Purchase #3	$167.29	10.467%	$184.8002	$184.80	$184.80	$184.80
Purchase #4	$61.49	5.339%	$64.773	$64.77	$64.75	$64.80
Purchase #5	$214.36	3.723%	$222.3406	$222.34	$222.35	$222.30
Purchase #6	$43.83	6.549%	$46.7004	$46.70	$46.70	$46.70
Purchase #7	$93.58	7.637%	$100.7267	$100.73	$100.75	$100.70
7 purchase totals =	$914.90		$998.0683	$998.07	$998.05	$998.10