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	$11.48	10.623%	$12.6995	$12.70	$12.70	$12.70
Purchase #2	$104.83	6.418%	$111.558	$111.56	$111.55	$111.60
Purchase #3	$172.80	13.813%	$196.6689	$196.67	$196.65	$196.70
Purchase #4	$83.75	9.828%	$91.981	$91.98	$92.00	$92.00
Purchase #5	$9.88	13.302%	$11.1942	$11.19	$11.20	$11.20
Purchase #6	$134.92	13.358%	$152.9426	$152.94	$152.95	$152.90
Purchase #7	$112.38	9.648%	$123.2224	$123.22	$123.20	$123.20
7 purchase totals =	$630.04		$700.2666	$700.26	$700.25	$700.30