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	$27.28	11.662%	$30.4614	$30.46	$30.45	$30.50
Purchase #2	$213.42	10.721%	$236.3008	$236.30	$236.30	$236.30
Purchase #3	$83.76	6.615%	$89.3007	$89.30	$89.30	$89.30
Purchase #4	$43.92	4.275%	$45.7976	$45.80	$45.80	$45.80
Purchase #5	$140.30	12.657%	$158.0578	$158.06	$158.05	$158.10
Purchase #6	$39.82	4.861%	$41.7557	$41.76	$41.75	$41.80
Purchase #7	$235.74	13.834%	$268.3523	$268.35	$268.35	$268.40
7 purchase totals =	$784.24		$870.0263	$870.03	$870.00	$870.20