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	$91.74	8.791%	$99.8049	$99.80	$99.80	$99.80
Purchase #2	$39.47	8.258%	$42.7294	$42.73	$42.75	$42.70
Purchase #3	$130.95	4.340%	$136.6332	$136.63	$136.65	$136.60
Purchase #4	$17.94	7.608%	$19.3049	$19.30	$19.30	$19.30
Purchase #5	$138.51	7.127%	$148.3816	$148.38	$148.40	$148.40
Purchase #6	$59.56	11.283%	$66.2802	$66.28	$66.30	$66.30
Purchase #7	$136.93	6.522%	$145.8606	$145.86	$145.85	$145.90
7 purchase totals =	$615.10		$658.9948	$658.98	$659.05	$659.00