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	$111.31	4.595%	$116.4247	$116.42	$116.40	$116.40
Purchase #2	$134.36	5.357%	$141.5577	$141.56	$141.55	$141.60
Purchase #3	$34.89	7.481%	$37.5001	$37.50	$37.50	$37.50
Purchase #4	$23.79	5.383%	$25.0706	$25.07	$25.05	$25.10
Purchase #5	$34.98	11.736%	$39.0853	$39.09	$39.10	$39.10
Purchase #6	$100.77	4.386%	$105.1898	$105.19	$105.20	$105.20
Purchase #7	$249.69	11.842%	$279.2583	$279.26	$279.25	$279.30
7 purchase totals =	$689.79		$744.0865	$744.09	$744.05	$744.20