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	$142.70	4.732%	$149.4526	$149.45	$149.45	$149.50
Purchase #2	$204.96	12.612%	$230.8096	$230.81	$230.80	$230.80
Purchase #3	$143.60	8.608%	$155.9611	$155.96	$155.95	$156.00
Purchase #4	$42.33	8.505%	$45.9302	$45.93	$45.95	$45.90
Purchase #5	$55.33	10.796%	$61.3034	$61.30	$61.30	$61.30
Purchase #6	$30.81	6.204%	$32.7215	$32.72	$32.70	$32.70
Purchase #7	$115.59	10.868%	$128.1523	$128.15	$128.15	$128.20
7 purchase totals =	$735.32		$804.3307	$804.32	$804.30	$804.40