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	$126.97	13.739%	$144.4144	$144.41	$144.40	$144.40
Purchase #2	$169.85	8.834%	$184.8545	$184.85	$184.85	$184.90
Purchase #3	$119.40	9.150%	$130.3251	$130.33	$130.35	$130.30
Purchase #4	$103.67	12.226%	$116.3447	$116.34	$116.35	$116.30
Purchase #5	$53.40	11.183%	$59.3717	$59.37	$59.35	$59.40
Purchase #6	$78.57	5.375%	$82.7931	$82.79	$82.80	$82.80
Purchase #7	$105.26	10.792%	$116.6197	$116.62	$116.60	$116.60
7 purchase totals =	$757.12		$834.7232	$834.71	$834.70	$834.70