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	$175.35	7.675%	$188.8081	$188.81	$188.80	$188.80
Purchase #2	$77.76	6.319%	$82.6737	$82.67	$82.65	$82.70
Purchase #3	$47.95	3.863%	$49.8023	$49.80	$49.80	$49.80
Purchase #4	$115.87	10.245%	$127.7409	$127.74	$127.75	$127.70
Purchase #5	$145.58	10.545%	$160.9314	$160.93	$160.95	$160.90
Purchase #6	$19.31	6.381%	$20.5422	$20.54	$20.55	$20.50
Purchase #7	$133.50	4.560%	$139.5876	$139.59	$139.60	$139.60
7 purchase totals =	$715.32		$770.0862	$770.08	$770.10	$770.00