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	$99.50	8.702%	$108.1585	$108.16	$108.15	$108.20
Purchase #2	$130.82	5.116%	$137.5128	$137.51	$137.50	$137.50
Purchase #3	$38.83	4.548%	$40.596	$40.60	$40.60	$40.60
Purchase #4	$135.52	7.838%	$146.1421	$146.14	$146.15	$146.10
Purchase #5	$237.90	3.680%	$246.6547	$246.65	$246.65	$246.70
Purchase #6	$213.29	12.584%	$240.1304	$240.13	$240.15	$240.10
Purchase #7	$144.67	4.770%	$151.5708	$151.57	$151.55	$151.60
7 purchase totals =	$1,000.53		$1,070.7653	$1,070.76	$1,070.75	$1,070.80