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	$27.67	3.322%	$28.5892	$28.59	$28.60	$28.60
Purchase #2	$123.28	11.330%	$137.2476	$137.25	$137.25	$137.20
Purchase #3	$90.72	9.527%	$99.3629	$99.36	$99.35	$99.40
Purchase #4	$36.41	6.361%	$38.726	$38.73	$38.75	$38.70
Purchase #5	$10.60	13.505%	$12.0315	$12.03	$12.05	$12.00
Purchase #6	$219.47	13.578%	$249.2696	$249.27	$249.25	$249.30
Purchase #7	$59.32	11.755%	$66.2931	$66.29	$66.30	$66.30
7 purchase totals =	$567.47		$631.5199	$631.52	$631.55	$631.50