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	$79.72	12.540%	$89.7169	$89.72	$89.70	$89.70
Purchase #2	$238.98	12.747%	$269.4428	$269.44	$269.45	$269.40
Purchase #3	$100.69	5.186%	$105.9118	$105.91	$105.90	$105.90
Purchase #4	$7.86	13.196%	$8.8972	$8.90	$8.90	$8.90
Purchase #5	$103.35	7.610%	$111.2149	$111.21	$111.20	$111.20
Purchase #6	$185.32	9.434%	$202.8031	$202.80	$202.80	$202.80
Purchase #7	$86.84	12.558%	$97.7454	$97.75	$97.75	$97.70
7 purchase totals =	$802.76		$885.7321	$885.73	$885.70	$885.60