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	$63.32	12.730%	$71.3806	$71.38	$71.40	$71.40
Purchase #2	$148.57	3.708%	$154.079	$154.08	$154.10	$154.10
Purchase #3	$40.41	12.484%	$45.4548	$45.45	$45.45	$45.50
Purchase #4	$143.92	10.314%	$158.7639	$158.76	$158.75	$158.80
Purchase #5	$173.75	12.511%	$195.4879	$195.49	$195.50	$195.50
Purchase #6	$49.38	13.772%	$56.1806	$56.18	$56.20	$56.20
Purchase #7	$28.86	11.361%	$32.1388	$32.14	$32.15	$32.10
7 purchase totals =	$648.21		$713.4856	$713.48	$713.55	$713.60