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	$97.70	12.631%	$110.0405	$110.04	$110.05	$110.00
Purchase #2	$121.85	10.676%	$134.8587	$134.86	$134.85	$134.90
Purchase #3	$41.91	4.669%	$43.8668	$43.87	$43.85	$43.90
Purchase #4	$211.81	4.869%	$222.123	$222.12	$222.10	$222.10
Purchase #5	$13.68	13.568%	$15.5361	$15.54	$15.55	$15.50
Purchase #6	$114.71	11.340%	$127.7181	$127.72	$127.70	$127.70
Purchase #7	$135.26	12.262%	$151.8456	$151.85	$151.85	$151.80
7 purchase totals =	$736.92		$805.9888	$806.00	$805.95	$805.90