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	$89.89	6.149%	$95.4173	$95.42	$95.40	$95.40
Purchase #2	$124.65	5.821%	$131.9059	$131.91	$131.90	$131.90
Purchase #3	$38.31	11.216%	$42.6068	$42.61	$42.60	$42.60
Purchase #4	$71.43	8.144%	$77.2473	$77.25	$77.25	$77.20
Purchase #5	$158.65	3.747%	$164.5946	$164.59	$164.60	$164.60
Purchase #6	$245.71	13.539%	$278.9767	$278.98	$279.00	$279.00
Purchase #7	$78.84	13.622%	$89.5796	$89.58	$89.60	$89.60
7 purchase totals =	$807.48		$880.3282	$880.34	$880.35	$880.30