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	$40.87	6.255%	$43.4264	$43.43	$43.45	$43.40
Purchase #2	$89.62	6.462%	$95.4112	$95.41	$95.40	$95.40
Purchase #3	$7.59	10.828%	$8.4118	$8.41	$8.40	$8.40
Purchase #4	$108.52	12.848%	$122.4626	$122.46	$122.45	$122.50
Purchase #5	$18.74	7.645%	$20.1727	$20.17	$20.15	$20.20
Purchase #6	$225.65	13.400%	$255.8871	$255.89	$255.90	$255.90
Purchase #7	$104.33	13.354%	$118.2622	$118.26	$118.25	$118.30
7 purchase totals =	$595.32		$664.0340	$664.03	$664.00	$664.10