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	$78.37	6.285%	$83.2956	$83.30	$83.30	$83.30
Purchase #2	$52.56	11.368%	$58.535	$58.54	$58.55	$58.50
Purchase #3	$24.63	3.598%	$25.5162	$25.52	$25.50	$25.50
Purchase #4	$138.91	12.764%	$156.6405	$156.64	$156.65	$156.60
Purchase #5	$250.38	6.466%	$266.5696	$266.57	$266.55	$266.60
Purchase #6	$83.93	9.301%	$91.7363	$91.74	$91.75	$91.70
Purchase #7	$176.78	4.852%	$185.3574	$185.36	$185.35	$185.40
7 purchase totals =	$805.56		$867.6506	$867.67	$867.65	$867.60