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	$236.96	4.795%	$248.3222	$248.32	$248.30	$248.30
Purchase #2	$142.64	7.289%	$153.037	$153.04	$153.05	$153.00
Purchase #3	$30.58	5.281%	$32.1949	$32.19	$32.20	$32.20
Purchase #4	$94.76	11.793%	$105.935	$105.94	$105.95	$105.90
Purchase #5	$172.87	4.193%	$180.1184	$180.12	$180.10	$180.10
Purchase #6	$146.81	12.716%	$165.4784	$165.48	$165.50	$165.50
Purchase #7	$151.52	13.632%	$172.1752	$172.18	$172.20	$172.20
7 purchase totals =	$976.14		$1,057.2611	$1,057.27	$1,057.30	$1,057.20