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	$9.92	7.841%	$10.6978	$10.70	$10.70	$10.70
Purchase #2	$143.71	11.587%	$160.3617	$160.36	$160.35	$160.40
Purchase #3	$33.87	10.652%	$37.4778	$37.48	$37.50	$37.50
Purchase #4	$157.78	9.447%	$172.6855	$172.69	$172.70	$172.70
Purchase #5	$103.57	9.402%	$113.3077	$113.31	$113.30	$113.30
Purchase #6	$49.73	8.669%	$54.0411	$54.04	$54.05	$54.00
Purchase #7	$10.54	3.277%	$10.8854	$10.89	$10.90	$10.90
7 purchase totals =	$509.12		$559.4570	$559.47	$559.50	$559.50