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	$105.30	5.815%	$111.4232	$111.42	$111.40	$111.40
Purchase #2	$217.36	5.506%	$229.3278	$229.33	$229.35	$229.30
Purchase #3	$135.97	10.640%	$150.4372	$150.44	$150.45	$150.40
Purchase #4	$69.99	9.327%	$76.518	$76.52	$76.50	$76.50
Purchase #5	$199.49	11.336%	$222.1042	$222.10	$222.10	$222.10
Purchase #6	$187.42	5.162%	$197.0946	$197.09	$197.10	$197.10
Purchase #7	$20.77	4.549%	$21.7148	$21.71	$21.70	$21.70
7 purchase totals =	$936.30		$1,008.6198	$1,008.61	$1,008.60	$1,008.50