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	$168.85	9.118%	$184.2457	$184.25	$184.25	$184.20
Purchase #2	$205.76	13.672%	$233.8915	$233.89	$233.90	$233.90
Purchase #3	$222.89	5.340%	$234.7923	$234.79	$234.80	$234.80
Purchase #4	$214.57	8.864%	$233.5895	$233.59	$233.60	$233.60
Purchase #5	$69.68	4.817%	$73.0365	$73.04	$73.05	$73.00
Purchase #6	$45.60	13.755%	$51.8723	$51.87	$51.85	$51.90
Purchase #7	$73.55	5.420%	$77.5364	$77.54	$77.55	$77.50
7 purchase totals =	$1,000.90		$1,088.9642	$1,088.97	$1,089.00	$1,088.90