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	$245.28	12.493%	$275.9228	$275.92	$275.90	$275.90
Purchase #2	$209.81	5.369%	$221.0747	$221.07	$221.05	$221.10
Purchase #3	$19.38	6.211%	$20.5837	$20.58	$20.60	$20.60
Purchase #4	$48.57	7.220%	$52.0768	$52.08	$52.10	$52.10
Purchase #5	$138.46	11.185%	$153.9468	$153.95	$153.95	$153.90
Purchase #6	$82.72	4.671%	$86.5839	$86.58	$86.60	$86.60
Purchase #7	$18.62	10.291%	$20.5362	$20.54	$20.55	$20.50
7 purchase totals =	$762.84		$830.7249	$830.72	$830.75	$830.70