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	$78.99	9.361%	$86.3843	$86.38	$86.40	$86.40
Purchase #2	$173.67	13.120%	$196.4555	$196.46	$196.45	$196.50
Purchase #3	$88.52	13.305%	$100.2976	$100.30	$100.30	$100.30
Purchase #4	$108.60	5.151%	$114.194	$114.19	$114.20	$114.20
Purchase #5	$226.46	4.550%	$236.7639	$236.76	$236.75	$236.80
Purchase #6	$90.68	13.774%	$103.1703	$103.17	$103.15	$103.20
Purchase #7	$151.43	7.202%	$162.336	$162.34	$162.35	$162.30
7 purchase totals =	$918.35		$999.6016	$999.60	$999.60	$999.70