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	$47.71	3.824%	$49.5344	$49.53	$49.55	$49.50
Purchase #2	$91.71	8.262%	$99.2871	$99.29	$99.30	$99.30
Purchase #3	$145.77	10.813%	$161.5321	$161.53	$161.55	$161.50
Purchase #4	$225.96	7.384%	$242.6449	$242.64	$242.65	$242.60
Purchase #5	$144.86	3.225%	$149.5317	$149.53	$149.55	$149.50
Purchase #6	$107.37	4.757%	$112.4776	$112.48	$112.50	$112.50
Purchase #7	$105.55	10.408%	$116.5356	$116.54	$116.55	$116.50
7 purchase totals =	$868.93		$931.5434	$931.54	$931.65	$931.40