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	$123.29	5.665%	$130.2744	$130.27	$130.25	$130.30
Purchase #2	$139.51	7.858%	$150.4727	$150.47	$150.45	$150.50
Purchase #3	$187.52	6.448%	$199.6113	$199.61	$199.60	$199.60
Purchase #4	$21.76	13.560%	$24.7107	$24.71	$24.70	$24.70
Purchase #5	$80.58	10.389%	$88.9515	$88.95	$88.95	$89.00
Purchase #6	$19.56	4.285%	$20.3981	$20.40	$20.40	$20.40
Purchase #7	$227.91	6.607%	$242.968	$242.97	$242.95	$243.00
7 purchase totals =	$800.13		$857.3867	$857.38	$857.30	$857.50