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	$208.62	10.389%	$230.2935	$230.29	$230.30	$230.30
Purchase #2	$134.87	8.433%	$146.2436	$146.24	$146.25	$146.20
Purchase #3	$45.73	5.332%	$48.1683	$48.17	$48.15	$48.20
Purchase #4	$210.25	11.585%	$234.6075	$234.61	$234.60	$234.60
Purchase #5	$29.42	10.254%	$32.4367	$32.44	$32.45	$32.40
Purchase #6	$194.48	7.782%	$209.6144	$209.61	$209.60	$209.60
Purchase #7	$172.80	4.105%	$179.8934	$179.89	$179.90	$179.90
7 purchase totals =	$996.17		$1,081.2574	$1,081.25	$1,081.25	$1,081.20