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	$193.59	10.181%	$213.2994	$213.30	$213.30	$213.30
Purchase #2	$158.76	5.561%	$167.5886	$167.59	$167.60	$167.60
Purchase #3	$159.85	5.244%	$168.2325	$168.23	$168.25	$168.20
Purchase #4	$70.68	13.391%	$80.1448	$80.14	$80.15	$80.10
Purchase #5	$145.37	9.796%	$159.6104	$159.61	$159.60	$159.60
Purchase #6	$87.54	3.211%	$90.3509	$90.35	$90.35	$90.40
Purchase #7	$54.82	10.452%	$60.5498	$60.55	$60.55	$60.50
7 purchase totals =	$870.61		$939.7764	$939.77	$939.80	$939.70