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	$163.80	13.202%	$185.4249	$185.42	$185.40	$185.40
Purchase #2	$106.25	5.677%	$112.2818	$112.28	$112.30	$112.30
Purchase #3	$18.71	9.661%	$20.5176	$20.52	$20.50	$20.50
Purchase #4	$237.69	4.793%	$249.0825	$249.08	$249.10	$249.10
Purchase #5	$200.35	12.188%	$224.7687	$224.77	$224.75	$224.80
Purchase #6	$128.92	10.369%	$142.2877	$142.29	$142.30	$142.30
Purchase #7	$31.85	11.250%	$35.4331	$35.43	$35.45	$35.40
7 purchase totals =	$887.57		$969.7963	$969.79	$969.80	$969.80