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	$6.29	12.461%	$7.0738	$7.07	$7.05	$7.10
Purchase #2	$212.70	5.734%	$224.8962	$224.90	$224.90	$224.90
Purchase #3	$6.92	4.254%	$7.2144	$7.21	$7.20	$7.20
Purchase #4	$142.30	5.147%	$149.6242	$149.62	$149.60	$149.60
Purchase #5	$94.28	5.490%	$99.456	$99.46	$99.45	$99.50
Purchase #6	$18.46	10.473%	$20.3933	$20.39	$20.40	$20.40
Purchase #7	$127.45	11.659%	$142.3094	$142.31	$142.30	$142.30
7 purchase totals =	$608.40		$650.9673	$650.96	$650.90	$651.00