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	$90.96	10.291%	$100.3207	$100.32	$100.30	$100.30
Purchase #2	$234.56	12.298%	$263.4062	$263.41	$263.40	$263.40
Purchase #3	$238.46	6.354%	$253.6117	$253.61	$253.60	$253.60
Purchase #4	$58.88	5.176%	$61.9276	$61.93	$61.95	$61.90
Purchase #5	$12.27	12.694%	$13.8276	$13.83	$13.85	$13.80
Purchase #6	$53.62	4.751%	$56.1675	$56.17	$56.15	$56.20
Purchase #7	$192.88	10.283%	$212.7139	$212.71	$212.70	$212.70
7 purchase totals =	$881.63		$961.9752	$961.98	$961.95	$961.90