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	$159.38	4.407%	$166.4039	$166.40	$166.40	$166.40
Purchase #2	$185.66	3.325%	$191.8332	$191.83	$191.85	$191.80
Purchase #3	$228.76	11.476%	$255.0125	$255.01	$255.00	$255.00
Purchase #4	$48.71	9.254%	$53.2176	$53.22	$53.20	$53.20
Purchase #5	$162.77	6.636%	$173.5714	$173.57	$173.55	$173.60
Purchase #6	$92.47	6.735%	$98.6979	$98.70	$98.70	$98.70
Purchase #7	$211.77	9.143%	$231.1321	$231.13	$231.15	$231.10
7 purchase totals =	$1,089.52		$1,169.8686	$1,169.86	$1,169.85	$1,169.80