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	$218.93	5.459%	$230.8814	$230.88	$230.90	$230.90
Purchase #2	$32.28	12.205%	$36.2198	$36.22	$36.20	$36.20
Purchase #3	$224.71	13.563%	$255.1874	$255.19	$255.20	$255.20
Purchase #4	$96.35	4.128%	$100.3273	$100.33	$100.35	$100.30
Purchase #5	$32.44	4.295%	$33.8333	$33.83	$33.85	$33.80
Purchase #6	$185.46	8.235%	$200.7326	$200.73	$200.75	$200.70
Purchase #7	$43.63	6.495%	$46.4638	$46.46	$46.45	$46.50
7 purchase totals =	$833.80		$903.6456	$903.64	$903.70	$903.60