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	$22.97	8.268%	$24.8692	$24.87	$24.85	$24.90
Purchase #2	$191.29	11.153%	$212.6246	$212.62	$212.60	$212.60
Purchase #3	$119.35	3.565%	$123.6048	$123.60	$123.60	$123.60
Purchase #4	$149.45	11.772%	$167.0433	$167.04	$167.05	$167.00
Purchase #5	$172.78	7.170%	$185.1683	$185.17	$185.15	$185.20
Purchase #6	$189.50	12.139%	$212.5034	$212.50	$212.50	$212.50
Purchase #7	$47.93	4.737%	$50.2004	$50.20	$50.20	$50.20
7 purchase totals =	$893.27		$976.0140	$976.00	$975.95	$976.00