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	$12.42	3.524%	$12.8577	$12.86	$12.85	$12.90
Purchase #2	$53.58	5.520%	$56.5376	$56.54	$56.55	$56.50
Purchase #3	$96.69	9.224%	$105.6087	$105.61	$105.60	$105.60
Purchase #4	$71.39	5.164%	$75.0766	$75.08	$75.10	$75.10
Purchase #5	$37.56	3.383%	$38.8307	$38.83	$38.85	$38.80
Purchase #6	$147.60	10.530%	$163.1423	$163.14	$163.15	$163.10
Purchase #7	$212.30	3.368%	$219.4503	$219.45	$219.45	$219.50
7 purchase totals =	$631.54		$671.5039	$671.51	$671.55	$671.50