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	$51.58	9.269%	$56.361	$56.36	$56.35	$56.40
Purchase #2	$105.93	6.207%	$112.5051	$112.51	$112.50	$112.50
Purchase #3	$53.69	4.856%	$56.2972	$56.30	$56.30	$56.30
Purchase #4	$65.26	7.267%	$70.0024	$70.00	$70.00	$70.00
Purchase #5	$18.70	11.118%	$20.7791	$20.78	$20.80	$20.80
Purchase #6	$91.73	13.433%	$104.0521	$104.05	$104.05	$104.10
Purchase #7	$96.72	3.874%	$100.4669	$100.47	$100.45	$100.50
7 purchase totals =	$483.61		$520.4638	$520.47	$520.45	$520.60