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	$91.58	9.472%	$100.2545	$100.25	$100.25	$100.30
Purchase #2	$245.26	3.293%	$253.3364	$253.34	$253.35	$253.30
Purchase #3	$96.51	7.214%	$103.4722	$103.47	$103.45	$103.50
Purchase #4	$161.57	10.603%	$178.7013	$178.70	$178.70	$178.70
Purchase #5	$171.33	8.350%	$185.6361	$185.64	$185.65	$185.60
Purchase #6	$39.93	13.464%	$45.3062	$45.31	$45.30	$45.30
Purchase #7	$39.89	4.241%	$41.5817	$41.58	$41.60	$41.60
7 purchase totals =	$846.07		$908.2884	$908.29	$908.30	$908.30