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	$41.54	12.713%	$46.821	$46.82	$46.80	$46.80
Purchase #2	$109.94	12.307%	$123.4703	$123.47	$123.45	$123.50
Purchase #3	$123.89	9.700%	$135.9073	$135.91	$135.90	$135.90
Purchase #4	$32.48	6.477%	$34.5837	$34.58	$34.60	$34.60
Purchase #5	$158.98	12.682%	$179.1418	$179.14	$179.15	$179.10
Purchase #6	$204.89	10.130%	$225.6454	$225.65	$225.65	$225.60
Purchase #7	$202.31	9.771%	$222.0777	$222.08	$222.10	$222.10
7 purchase totals =	$874.03		$967.6472	$967.65	$967.65	$967.60