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	$174.43	8.247%	$188.8152	$188.82	$188.80	$188.80
Purchase #2	$220.72	4.685%	$231.0607	$231.06	$231.05	$231.10
Purchase #3	$94.41	6.359%	$100.4135	$100.41	$100.40	$100.40
Purchase #4	$34.61	10.547%	$38.2603	$38.26	$38.25	$38.30
Purchase #5	$25.82	10.397%	$28.5045	$28.50	$28.50	$28.50
Purchase #6	$12.34	3.695%	$12.796	$12.80	$12.80	$12.80
Purchase #7	$88.85	11.608%	$99.1637	$99.16	$99.15	$99.20
7 purchase totals =	$651.18		$699.0139	$699.01	$698.95	$699.10