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	$233.28	10.868%	$258.6329	$258.63	$258.65	$258.60
Purchase #2	$122.53	6.112%	$130.019	$130.02	$130.00	$130.00
Purchase #3	$206.51	7.672%	$222.3534	$222.35	$222.35	$222.40
Purchase #4	$166.32	5.660%	$175.7337	$175.73	$175.75	$175.70
Purchase #5	$103.84	7.393%	$111.5169	$111.52	$111.50	$111.50
Purchase #6	$29.72	13.701%	$33.7919	$33.79	$33.80	$33.80
Purchase #7	$60.40	13.475%	$68.5389	$68.54	$68.55	$68.50
7 purchase totals =	$922.60		$1,000.5867	$1,000.58	$1,000.60	$1,000.50