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	$45.89	11.808%	$51.3087	$51.31	$51.30	$51.30
Purchase #2	$10.40	13.617%	$11.8162	$11.82	$11.80	$11.80
Purchase #3	$99.69	12.506%	$112.1572	$112.16	$112.15	$112.20
Purchase #4	$116.66	10.139%	$128.4882	$128.49	$128.50	$128.50
Purchase #5	$64.30	9.729%	$70.5557	$70.56	$70.55	$70.60
Purchase #6	$156.79	10.488%	$173.2341	$173.23	$173.25	$173.20
Purchase #7	$250.45	3.823%	$260.0247	$260.02	$260.00	$260.00
7 purchase totals =	$744.18		$807.5848	$807.59	$807.55	$807.60