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	$49.60	10.755%	$54.9345	$54.93	$54.95	$54.90
Purchase #2	$146.50	8.157%	$158.45	$158.45	$158.45	$158.50
Purchase #3	$80.55	6.328%	$85.6472	$85.65	$85.65	$85.60
Purchase #4	$159.82	7.841%	$172.3515	$172.35	$172.35	$172.40
Purchase #5	$242.71	6.192%	$257.7386	$257.74	$257.75	$257.70
Purchase #6	$77.45	6.410%	$82.4145	$82.41	$82.40	$82.40
Purchase #7	$42.70	3.689%	$44.2752	$44.28	$44.30	$44.30
7 purchase totals =	$799.33		$855.8115	$855.81	$855.85	$855.80