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	$70.72	10.437%	$78.101	$78.10	$78.10	$78.10
Purchase #2	$156.94	13.480%	$178.0955	$178.10	$178.10	$178.10
Purchase #3	$21.41	12.339%	$24.0518	$24.05	$24.05	$24.10
Purchase #4	$113.33	4.317%	$118.2225	$118.22	$118.20	$118.20
Purchase #5	$8.94	13.484%	$10.1455	$10.15	$10.15	$10.10
Purchase #6	$48.42	3.851%	$50.2847	$50.28	$50.30	$50.30
Purchase #7	$71.62	8.831%	$77.9448	$77.94	$77.95	$77.90
7 purchase totals =	$491.38		$536.8458	$536.84	$536.85	$536.80