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	$171.37	8.238%	$185.4875	$185.49	$185.50	$185.50
Purchase #2	$233.69	6.395%	$248.6345	$248.63	$248.65	$248.60
Purchase #3	$105.89	13.155%	$119.8198	$119.82	$119.80	$119.80
Purchase #4	$173.55	12.278%	$194.8585	$194.86	$194.85	$194.90
Purchase #5	$249.47	11.617%	$278.4509	$278.45	$278.45	$278.50
Purchase #6	$103.37	3.609%	$107.1006	$107.10	$107.10	$107.10
Purchase #7	$47.82	10.497%	$52.8397	$52.84	$52.85	$52.80
7 purchase totals =	$1,085.16		$1,187.1915	$1,187.19	$1,187.20	$1,187.20