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	$34.31	7.621%	$36.9248	$36.92	$36.90	$36.90
Purchase #2	$44.58	12.737%	$50.2582	$50.26	$50.25	$50.30
Purchase #3	$18.39	3.601%	$19.0522	$19.05	$19.05	$19.10
Purchase #4	$43.47	5.481%	$45.8526	$45.85	$45.85	$45.90
Purchase #5	$92.70	8.710%	$100.7742	$100.77	$100.75	$100.80
Purchase #6	$35.89	8.755%	$39.0322	$39.03	$39.05	$39.00
Purchase #7	$166.79	12.615%	$187.8306	$187.83	$187.85	$187.80
7 purchase totals =	$436.13		$479.7248	$479.71	$479.70	$479.80