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	$39.92	6.277%	$42.4258	$42.43	$42.45	$42.40
Purchase #2	$43.71	7.326%	$46.9122	$46.91	$46.90	$46.90
Purchase #3	$50.89	4.343%	$53.1002	$53.10	$53.10	$53.10
Purchase #4	$102.74	4.520%	$107.3838	$107.38	$107.40	$107.40
Purchase #5	$226.27	11.838%	$253.0558	$253.06	$253.05	$253.10
Purchase #6	$167.74	13.803%	$190.8932	$190.89	$190.90	$190.90
Purchase #7	$110.88	5.150%	$116.5903	$116.59	$116.60	$116.60
7 purchase totals =	$742.15		$810.3613	$810.36	$810.40	$810.40