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	$54.61	8.688%	$59.3545	$59.35	$59.35	$59.40
Purchase #2	$37.39	4.732%	$39.1593	$39.16	$39.15	$39.20
Purchase #3	$86.66	5.826%	$91.7088	$91.71	$91.70	$91.70
Purchase #4	$197.34	11.293%	$219.6256	$219.63	$219.65	$219.60
Purchase #5	$60.83	7.668%	$65.4944	$65.49	$65.50	$65.50
Purchase #6	$23.87	3.105%	$24.6112	$24.61	$24.60	$24.60
Purchase #7	$95.57	8.117%	$103.3274	$103.33	$103.35	$103.30
7 purchase totals =	$556.27		$603.2812	$603.28	$603.30	$603.30