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	$36.50	4.345%	$38.0859	$38.09	$38.10	$38.10
Purchase #2	$247.83	12.720%	$279.354	$279.35	$279.35	$279.40
Purchase #3	$151.63	3.192%	$156.47	$156.47	$156.45	$156.50
Purchase #4	$244.96	5.163%	$257.6073	$257.61	$257.60	$257.60
Purchase #5	$223.79	7.464%	$240.4937	$240.49	$240.50	$240.50
Purchase #6	$78.90	9.542%	$86.4286	$86.43	$86.45	$86.40
Purchase #7	$11.98	5.807%	$12.6757	$12.68	$12.70	$12.70
7 purchase totals =	$995.59		$1,071.1152	$1,071.12	$1,071.15	$1,071.20