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	$62.92	5.278%	$66.2409	$66.24	$66.25	$66.20
Purchase #2	$214.40	13.738%	$243.8543	$243.85	$243.85	$243.90
Purchase #3	$195.26	5.804%	$206.5929	$206.59	$206.60	$206.60
Purchase #4	$141.76	8.475%	$153.7742	$153.77	$153.75	$153.80
Purchase #5	$99.59	12.322%	$111.8615	$111.86	$111.85	$111.90
Purchase #6	$24.32	3.243%	$25.1087	$25.11	$25.10	$25.10
Purchase #7	$39.72	3.429%	$41.082	$41.08	$41.10	$41.10
7 purchase totals =	$777.97		$848.5145	$848.50	$848.50	$848.60