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	$72.28	11.243%	$80.4064	$80.41	$80.40	$80.40
Purchase #2	$43.34	4.870%	$45.4507	$45.45	$45.45	$45.50
Purchase #3	$46.39	13.475%	$52.6411	$52.64	$52.65	$52.60
Purchase #4	$241.75	13.821%	$275.1623	$275.16	$275.15	$275.20
Purchase #5	$239.80	3.462%	$248.1019	$248.10	$248.10	$248.10
Purchase #6	$28.79	13.339%	$32.6303	$32.63	$32.65	$32.60
Purchase #7	$95.43	5.573%	$100.7483	$100.75	$100.75	$100.70
7 purchase totals =	$767.78		$835.1410	$835.14	$835.15	$835.10