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	$28.85	3.644%	$29.9013	$29.90	$29.90	$29.90
Purchase #2	$178.86	5.769%	$189.1784	$189.18	$189.20	$189.20
Purchase #3	$191.73	13.474%	$217.5637	$217.56	$217.55	$217.60
Purchase #4	$103.47	13.769%	$117.7168	$117.72	$117.70	$117.70
Purchase #5	$105.27	6.184%	$111.7799	$111.78	$111.80	$111.80
Purchase #6	$62.74	4.482%	$65.552	$65.55	$65.55	$65.60
Purchase #7	$111.86	9.603%	$122.6019	$122.60	$122.60	$122.60
7 purchase totals =	$782.78		$854.2940	$854.29	$854.30	$854.40