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	$37.35	3.444%	$38.6363	$38.64	$38.65	$38.60
Purchase #2	$140.40	3.339%	$145.088	$145.09	$145.10	$145.10
Purchase #3	$41.65	4.648%	$43.5859	$43.59	$43.60	$43.60
Purchase #4	$185.36	3.857%	$192.5093	$192.51	$192.50	$192.50
Purchase #5	$57.55	4.740%	$60.2779	$60.28	$60.30	$60.30
Purchase #6	$120.48	5.786%	$127.451	$127.45	$127.45	$127.50
Purchase #7	$130.99	6.397%	$139.3694	$139.37	$139.35	$139.40
7 purchase totals =	$713.78		$746.9178	$746.93	$746.95	$747.00