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	$49.55	10.167%	$54.5877	$54.59	$54.60	$54.60
Purchase #2	$48.71	4.542%	$50.9224	$50.92	$50.90	$50.90
Purchase #3	$55.88	9.564%	$61.2244	$61.22	$61.20	$61.20
Purchase #4	$58.96	7.807%	$63.563	$63.56	$63.55	$63.60
Purchase #5	$138.65	9.608%	$151.9715	$151.97	$151.95	$152.00
Purchase #6	$29.33	10.355%	$32.3671	$32.37	$32.35	$32.40
Purchase #7	$147.88	5.525%	$156.0504	$156.05	$156.05	$156.10
7 purchase totals =	$528.96		$570.6865	$570.68	$570.60	$570.80