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	$59.38	9.688%	$65.1327	$65.13	$65.15	$65.10
Purchase #2	$46.86	8.556%	$50.8693	$50.87	$50.85	$50.90
Purchase #3	$56.85	8.866%	$61.8903	$61.89	$61.90	$61.90
Purchase #4	$91.70	12.492%	$103.1552	$103.16	$103.15	$103.20
Purchase #5	$13.98	7.147%	$14.9792	$14.98	$15.00	$15.00
Purchase #6	$106.62	7.289%	$114.3915	$114.39	$114.40	$114.40
Purchase #7	$232.95	11.837%	$260.5243	$260.52	$260.50	$260.50
7 purchase totals =	$608.34		$670.9425	$670.94	$670.95	$671.00