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	$203.70	10.161%	$224.398	$224.40	$224.40	$224.40
Purchase #2	$128.76	8.170%	$139.2797	$139.28	$139.30	$139.30
Purchase #3	$150.67	10.410%	$166.3547	$166.35	$166.35	$166.40
Purchase #4	$97.73	13.531%	$110.9538	$110.95	$110.95	$111.00
Purchase #5	$173.56	13.273%	$196.5966	$196.60	$196.60	$196.60
Purchase #6	$129.56	12.610%	$145.8975	$145.90	$145.90	$145.90
Purchase #7	$234.84	13.750%	$267.1305	$267.13	$267.15	$267.10
7 purchase totals =	$1,118.82		$1,250.6108	$1,250.61	$1,250.65	$1,250.70