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	$12.47	5.739%	$13.1857	$13.19	$13.20	$13.20
Purchase #2	$156.38	12.598%	$176.0808	$176.08	$176.10	$176.10
Purchase #3	$127.50	7.107%	$136.5614	$136.56	$136.55	$136.60
Purchase #4	$35.88	3.179%	$37.0206	$37.02	$37.00	$37.00
Purchase #5	$249.72	10.688%	$276.4101	$276.41	$276.40	$276.40
Purchase #6	$51.71	11.791%	$57.8071	$57.81	$57.80	$57.80
Purchase #7	$103.79	5.444%	$109.4403	$109.44	$109.45	$109.40
7 purchase totals =	$737.45		$806.5060	$806.51	$806.50	$806.50