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	$72.37	10.804%	$80.1889	$80.19	$80.20	$80.20
Purchase #2	$35.68	8.111%	$38.574	$38.57	$38.55	$38.60
Purchase #3	$66.80	7.437%	$71.7679	$71.77	$71.75	$71.80
Purchase #4	$228.25	8.688%	$248.0804	$248.08	$248.10	$248.10
Purchase #5	$52.58	13.112%	$59.4743	$59.47	$59.45	$59.50
Purchase #6	$91.71	9.725%	$100.6288	$100.63	$100.65	$100.60
Purchase #7	$141.25	10.146%	$155.5812	$155.58	$155.60	$155.60
7 purchase totals =	$688.64		$754.2955	$754.29	$754.30	$754.40