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	$35.98	9.193%	$39.2876	$39.29	$39.30	$39.30
Purchase #2	$61.68	13.330%	$69.9019	$69.90	$69.90	$69.90
Purchase #3	$100.44	4.137%	$104.5952	$104.60	$104.60	$104.60
Purchase #4	$29.28	12.145%	$32.8361	$32.84	$32.85	$32.80
Purchase #5	$190.38	13.713%	$216.4868	$216.49	$216.50	$216.50
Purchase #6	$16.62	10.837%	$18.4211	$18.42	$18.40	$18.40
Purchase #7	$151.87	13.462%	$172.3147	$172.31	$172.30	$172.30
7 purchase totals =	$586.25		$653.8434	$653.85	$653.85	$653.80