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	$95.48	4.739%	$100.0048	$100.00	$100.00	$100.00
Purchase #2	$34.36	9.497%	$37.6232	$37.62	$37.60	$37.60
Purchase #3	$95.44	9.854%	$104.8447	$104.84	$104.85	$104.80
Purchase #4	$128.50	13.228%	$145.498	$145.50	$145.50	$145.50
Purchase #5	$6.63	10.520%	$7.3275	$7.33	$7.35	$7.30
Purchase #6	$99.52	4.275%	$103.7745	$103.77	$103.75	$103.80
Purchase #7	$37.86	5.274%	$39.8567	$39.86	$39.85	$39.90
7 purchase totals =	$497.79		$538.9294	$538.92	$538.90	$538.90