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	$165.55	10.119%	$182.302	$182.30	$182.30	$182.30
Purchase #2	$66.70	12.154%	$74.8067	$74.81	$74.80	$74.80
Purchase #3	$120.26	6.195%	$127.7101	$127.71	$127.70	$127.70
Purchase #4	$80.52	10.787%	$89.2057	$89.21	$89.20	$89.20
Purchase #5	$122.95	13.404%	$139.4302	$139.43	$139.45	$139.40
Purchase #6	$138.49	7.267%	$148.5541	$148.55	$148.55	$148.60
Purchase #7	$96.55	8.260%	$104.525	$104.53	$104.55	$104.50
7 purchase totals =	$791.02		$866.5338	$866.54	$866.55	$866.50