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	$189.25	12.826%	$213.5232	$213.52	$213.50	$213.50
Purchase #2	$54.89	9.823%	$60.2818	$60.28	$60.30	$60.30
Purchase #3	$117.70	5.203%	$123.8239	$123.82	$123.80	$123.80
Purchase #4	$88.40	3.198%	$91.227	$91.23	$91.25	$91.20
Purchase #5	$77.30	3.714%	$80.1709	$80.17	$80.15	$80.20
Purchase #6	$48.72	3.803%	$50.5728	$50.57	$50.55	$50.60
Purchase #7	$98.94	11.749%	$110.5645	$110.56	$110.55	$110.60
7 purchase totals =	$675.20		$730.1641	$730.15	$730.10	$730.20