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	$239.76	4.555%	$250.6811	$250.68	$250.70	$250.70
Purchase #2	$130.31	11.107%	$144.7835	$144.78	$144.80	$144.80
Purchase #3	$78.81	13.553%	$89.4911	$89.49	$89.50	$89.50
Purchase #4	$106.54	12.729%	$120.1015	$120.10	$120.10	$120.10
Purchase #5	$89.62	12.309%	$100.6513	$100.65	$100.65	$100.70
Purchase #6	$88.64	13.585%	$100.6817	$100.68	$100.70	$100.70
Purchase #7	$204.80	3.186%	$211.3249	$211.32	$211.30	$211.30
7 purchase totals =	$938.48		$1,017.7151	$1,017.70	$1,017.75	$1,017.80