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	$97.79	5.623%	$103.2887	$103.29	$103.30	$103.30
Purchase #2	$235.92	8.102%	$255.0342	$255.03	$255.05	$255.00
Purchase #3	$218.55	5.417%	$230.3889	$230.39	$230.40	$230.40
Purchase #4	$61.49	7.849%	$66.3164	$66.32	$66.30	$66.30
Purchase #5	$77.71	6.687%	$82.9065	$82.91	$82.90	$82.90
Purchase #6	$30.75	3.410%	$31.7986	$31.80	$31.80	$31.80
Purchase #7	$120.91	13.581%	$137.3308	$137.33	$137.35	$137.30
7 purchase totals =	$843.12		$907.0641	$907.07	$907.10	$907.00