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	$214.51	12.413%	$241.1371	$241.14	$241.15	$241.10
Purchase #2	$88.88	11.451%	$99.0576	$99.06	$99.05	$99.10
Purchase #3	$108.52	9.713%	$119.0605	$119.06	$119.05	$119.10
Purchase #4	$236.43	8.343%	$256.1554	$256.16	$256.15	$256.20
Purchase #5	$77.45	7.757%	$83.4578	$83.46	$83.45	$83.50
Purchase #6	$162.91	5.135%	$171.2754	$171.28	$171.30	$171.30
Purchase #7	$6.91	3.813%	$7.1735	$7.17	$7.15	$7.20
7 purchase totals =	$895.61		$977.3173	$977.33	$977.30	$977.50