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	$30.54	9.488%	$33.4376	$33.44	$33.45	$33.40
Purchase #2	$136.69	8.605%	$148.4522	$148.45	$148.45	$148.50
Purchase #3	$162.31	6.286%	$172.5128	$172.51	$172.50	$172.50
Purchase #4	$63.42	3.115%	$65.3955	$65.40	$65.40	$65.40
Purchase #5	$180.80	4.858%	$189.5833	$189.58	$189.60	$189.60
Purchase #6	$112.81	3.346%	$116.5846	$116.58	$116.60	$116.60
Purchase #7	$242.76	4.518%	$253.7279	$253.73	$253.75	$253.70
7 purchase totals =	$929.33		$979.6939	$979.69	$979.75	$979.70