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	$126.60	8.671%	$137.5775	$137.58	$137.60	$137.60
Purchase #2	$56.52	3.103%	$58.2738	$58.27	$58.25	$58.30
Purchase #3	$42.99	7.280%	$46.1197	$46.12	$46.10	$46.10
Purchase #4	$139.88	4.684%	$146.432	$146.43	$146.45	$146.40
Purchase #5	$65.91	8.592%	$71.573	$71.57	$71.55	$71.60
Purchase #6	$41.46	3.692%	$42.9907	$42.99	$43.00	$43.00
Purchase #7	$151.46	9.282%	$165.5185	$165.52	$165.50	$165.50
7 purchase totals =	$624.82		$668.4852	$668.48	$668.45	$668.50