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	$55.79	8.810%	$60.7051	$60.71	$60.70	$60.70
Purchase #2	$55.65	10.239%	$61.348	$61.35	$61.35	$61.30
Purchase #3	$140.79	9.346%	$153.9482	$153.95	$153.95	$153.90
Purchase #4	$82.30	9.813%	$90.3761	$90.38	$90.40	$90.40
Purchase #5	$49.57	8.819%	$53.9416	$53.94	$53.95	$53.90
Purchase #6	$124.32	3.463%	$128.6252	$128.63	$128.65	$128.60
Purchase #7	$48.96	8.333%	$53.0398	$53.04	$53.05	$53.00
7 purchase totals =	$557.38		$601.9840	$602.00	$602.05	$601.80