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	$15.32	11.463%	$17.0761	$17.08	$17.10	$17.10
Purchase #2	$151.84	13.810%	$172.8091	$172.81	$172.80	$172.80
Purchase #3	$100.57	7.441%	$108.0534	$108.05	$108.05	$108.10
Purchase #4	$203.30	11.528%	$226.7364	$226.74	$226.75	$226.70
Purchase #5	$38.51	11.567%	$42.9645	$42.96	$42.95	$43.00
Purchase #6	$101.63	8.161%	$109.924	$109.92	$109.90	$109.90
Purchase #7	$55.29	7.349%	$59.3533	$59.35	$59.35	$59.40
7 purchase totals =	$666.46		$736.9168	$736.91	$736.90	$737.00