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	$79.43	4.425%	$82.9448	$82.94	$82.95	$82.90
Purchase #2	$34.86	7.409%	$37.4428	$37.44	$37.45	$37.40
Purchase #3	$27.96	7.403%	$30.0299	$30.03	$30.05	$30.00
Purchase #4	$103.52	3.232%	$106.8658	$106.87	$106.85	$106.90
Purchase #5	$174.49	6.514%	$185.8563	$185.86	$185.85	$185.90
Purchase #6	$18.42	6.218%	$19.5654	$19.57	$19.55	$19.60
Purchase #7	$87.98	8.513%	$95.4697	$95.47	$95.45	$95.50
7 purchase totals =	$526.66		$558.1747	$558.18	$558.15	$558.20