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	$46.79	7.281%	$50.1968	$50.20	$50.20	$50.20
Purchase #2	$111.67	3.692%	$115.7929	$115.79	$115.80	$115.80
Purchase #3	$190.72	5.300%	$200.8282	$200.83	$200.85	$200.80
Purchase #4	$49.61	9.576%	$54.3607	$54.36	$54.35	$54.40
Purchase #5	$95.72	10.253%	$105.5342	$105.53	$105.55	$105.50
Purchase #6	$174.30	8.556%	$189.2131	$189.21	$189.20	$189.20
Purchase #7	$244.27	3.780%	$253.5034	$253.50	$253.50	$253.50
7 purchase totals =	$913.08		$969.4293	$969.42	$969.45	$969.40