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	$138.72	8.729%	$150.8289	$150.83	$150.85	$150.80
Purchase #2	$210.41	3.414%	$217.5934	$217.59	$217.60	$217.60
Purchase #3	$231.73	10.491%	$256.0408	$256.04	$256.05	$256.00
Purchase #4	$142.85	4.412%	$149.1525	$149.15	$149.15	$149.20
Purchase #5	$24.32	5.770%	$25.7233	$25.72	$25.70	$25.70
Purchase #6	$241.27	10.785%	$267.291	$267.29	$267.30	$267.30
Purchase #7	$6.93	13.513%	$7.8665	$7.87	$7.85	$7.90
7 purchase totals =	$996.23		$1,074.4964	$1,074.49	$1,074.50	$1,074.50