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	$101.96	3.780%	$105.8141	$105.81	$105.80	$105.80
Purchase #2	$209.45	4.490%	$218.8543	$218.85	$218.85	$218.90
Purchase #3	$145.70	5.215%	$153.2983	$153.30	$153.30	$153.30
Purchase #4	$138.70	5.204%	$145.9179	$145.92	$145.90	$145.90
Purchase #5	$112.57	3.335%	$116.3242	$116.32	$116.30	$116.30
Purchase #6	$232.74	12.713%	$262.3282	$262.33	$262.35	$262.30
Purchase #7	$247.78	11.133%	$275.3653	$275.37	$275.35	$275.40
7 purchase totals =	$1,188.90		$1,277.9023	$1,277.90	$1,277.85	$1,277.90