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	$83.78	6.743%	$89.4293	$89.43	$89.45	$89.40
Purchase #2	$72.85	5.408%	$76.7897	$76.79	$76.80	$76.80
Purchase #3	$163.91	11.303%	$182.4367	$182.44	$182.45	$182.40
Purchase #4	$139.44	3.809%	$144.7513	$144.75	$144.75	$144.80
Purchase #5	$158.25	13.589%	$179.7546	$179.75	$179.75	$179.80
Purchase #6	$145.85	5.219%	$153.4619	$153.46	$153.45	$153.50
Purchase #7	$79.44	4.840%	$83.2849	$83.28	$83.30	$83.30
7 purchase totals =	$843.52		$909.9084	$909.90	$909.95	$910.00