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	$50.32	5.154%	$52.9135	$52.91	$52.90	$52.90
Purchase #2	$105.61	8.168%	$114.2362	$114.24	$114.25	$114.20
Purchase #3	$149.77	8.493%	$162.49	$162.49	$162.50	$162.50
Purchase #4	$232.98	10.461%	$257.352	$257.35	$257.35	$257.40
Purchase #5	$103.49	4.589%	$108.2392	$108.24	$108.25	$108.20
Purchase #6	$70.71	11.543%	$78.8721	$78.87	$78.85	$78.90
Purchase #7	$65.78	6.471%	$70.0366	$70.04	$70.05	$70.00
7 purchase totals =	$778.66		$844.1396	$844.14	$844.15	$844.10