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	$30.52	10.168%	$33.6233	$33.62	$33.60	$33.60
Purchase #2	$40.65	4.192%	$42.354	$42.35	$42.35	$42.40
Purchase #3	$246.89	13.122%	$279.2869	$279.29	$279.30	$279.30
Purchase #4	$48.92	9.340%	$53.4891	$53.49	$53.50	$53.50
Purchase #5	$43.29	13.711%	$49.2255	$49.23	$49.25	$49.20
Purchase #6	$97.35	11.586%	$108.629	$108.63	$108.65	$108.60
Purchase #7	$95.49	5.314%	$100.5643	$100.56	$100.55	$100.60
7 purchase totals =	$603.11		$667.1721	$667.17	$667.20	$667.20