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	$68.35	9.386%	$74.7653	$74.77	$74.75	$74.80
Purchase #2	$165.39	9.729%	$181.4808	$181.48	$181.50	$181.50
Purchase #3	$153.70	10.336%	$169.5864	$169.59	$169.60	$169.60
Purchase #4	$71.59	11.562%	$79.8672	$79.87	$79.85	$79.90
Purchase #5	$88.79	12.666%	$100.0361	$100.04	$100.05	$100.00
Purchase #6	$15.92	11.144%	$17.6941	$17.69	$17.70	$17.70
Purchase #7	$129.32	10.208%	$142.521	$142.52	$142.50	$142.50
7 purchase totals =	$693.06		$765.9509	$765.96	$765.95	$766.00