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	$76.82	4.549%	$80.3145	$80.31	$80.30	$80.30
Purchase #2	$9.30	13.442%	$10.5501	$10.55	$10.55	$10.60
Purchase #3	$248.91	10.658%	$275.4388	$275.44	$275.45	$275.40
Purchase #4	$9.78	8.810%	$10.6416	$10.64	$10.65	$10.60
Purchase #5	$145.67	6.520%	$155.1677	$155.17	$155.15	$155.20
Purchase #6	$36.38	10.769%	$40.2978	$40.30	$40.30	$40.30
Purchase #7	$74.62	9.597%	$81.7813	$81.78	$81.80	$81.80
7 purchase totals =	$601.48		$654.1918	$654.19	$654.20	$654.20