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	$239.68	11.851%	$268.0845	$268.08	$268.10	$268.10
Purchase #2	$178.71	9.739%	$196.1146	$196.11	$196.10	$196.10
Purchase #3	$216.83	11.672%	$242.1384	$242.14	$242.15	$242.10
Purchase #4	$190.62	7.338%	$204.6077	$204.61	$204.60	$204.60
Purchase #5	$133.82	8.352%	$144.9966	$145.00	$145.00	$145.00
Purchase #6	$59.31	3.531%	$61.4042	$61.40	$61.40	$61.40
Purchase #7	$171.85	5.540%	$181.3705	$181.37	$181.35	$181.40
7 purchase totals =	$1,190.82		$1,298.7165	$1,298.71	$1,298.70	$1,298.70