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	$146.49	4.347%	$152.8579	$152.86	$152.85	$152.90
Purchase #2	$123.69	13.654%	$140.5786	$140.58	$140.60	$140.60
Purchase #3	$169.28	5.582%	$178.7292	$178.73	$178.75	$178.70
Purchase #4	$114.72	13.745%	$130.4883	$130.49	$130.50	$130.50
Purchase #5	$165.54	9.388%	$181.0809	$181.08	$181.10	$181.10
Purchase #6	$62.64	7.255%	$67.1845	$67.18	$67.20	$67.20
Purchase #7	$84.63	6.118%	$89.8077	$89.81	$89.80	$89.80
7 purchase totals =	$866.99		$940.7271	$940.73	$940.80	$940.80