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	$143.78	12.852%	$162.2586	$162.26	$162.25	$162.30
Purchase #2	$38.26	11.446%	$42.6392	$42.64	$42.65	$42.60
Purchase #3	$111.40	3.569%	$115.3759	$115.38	$115.40	$115.40
Purchase #4	$29.78	13.612%	$33.8337	$33.83	$33.85	$33.80
Purchase #5	$207.90	13.406%	$235.7711	$235.77	$235.75	$235.80
Purchase #6	$50.29	4.139%	$52.3715	$52.37	$52.35	$52.40
Purchase #7	$172.85	6.865%	$184.7162	$184.72	$184.70	$184.70
7 purchase totals =	$754.26		$826.9662	$826.97	$826.95	$827.00