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	$18.55	9.578%	$20.3267	$20.33	$20.35	$20.30
Purchase #2	$179.99	9.245%	$196.6301	$196.63	$196.65	$196.60
Purchase #3	$243.38	13.341%	$275.8493	$275.85	$275.85	$275.80
Purchase #4	$138.46	12.786%	$156.1635	$156.16	$156.15	$156.20
Purchase #5	$126.75	5.404%	$133.5996	$133.60	$133.60	$133.60
Purchase #6	$189.28	8.582%	$205.524	$205.52	$205.50	$205.50
Purchase #7	$154.81	5.218%	$162.888	$162.89	$162.90	$162.90
7 purchase totals =	$1,051.22		$1,150.9812	$1,150.98	$1,151.00	$1,150.90