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	$80.94	10.485%	$89.4266	$89.43	$89.45	$89.40
Purchase #2	$88.60	3.242%	$91.4724	$91.47	$91.45	$91.50
Purchase #3	$152.66	4.483%	$159.5037	$159.50	$159.50	$159.50
Purchase #4	$73.47	10.768%	$81.3812	$81.38	$81.40	$81.40
Purchase #5	$197.58	4.403%	$206.2794	$206.28	$206.30	$206.30
Purchase #6	$180.86	6.793%	$193.1458	$193.15	$193.15	$193.10
Purchase #7	$128.45	12.453%	$144.4459	$144.45	$144.45	$144.40
7 purchase totals =	$902.56		$965.6550	$965.66	$965.70	$965.60