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	$60.80	12.869%	$68.6244	$68.62	$68.60	$68.60
Purchase #2	$231.52	9.429%	$253.35	$253.35	$253.35	$253.40
Purchase #3	$31.74	4.867%	$33.2848	$33.28	$33.30	$33.30
Purchase #4	$165.57	12.289%	$185.9169	$185.92	$185.90	$185.90
Purchase #5	$82.83	10.854%	$91.8204	$91.82	$91.80	$91.80
Purchase #6	$118.27	11.721%	$132.1324	$132.13	$132.15	$132.10
Purchase #7	$28.31	13.226%	$32.0543	$32.05	$32.05	$32.10
7 purchase totals =	$719.04		$797.1832	$797.17	$797.15	$797.20