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	$138.52	3.363%	$143.1784	$143.18	$143.20	$143.20
Purchase #2	$72.29	8.539%	$78.4628	$78.46	$78.45	$78.50
Purchase #3	$78.50	13.753%	$89.2961	$89.30	$89.30	$89.30
Purchase #4	$123.52	10.345%	$136.2981	$136.30	$136.30	$136.30
Purchase #5	$247.88	7.142%	$265.5836	$265.58	$265.60	$265.60
Purchase #6	$144.40	12.722%	$162.7706	$162.77	$162.75	$162.80
Purchase #7	$50.64	6.596%	$53.9802	$53.98	$54.00	$54.00
7 purchase totals =	$855.75		$929.5698	$929.57	$929.60	$929.70