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	$108.84	8.530%	$118.1241	$118.12	$118.10	$118.10
Purchase #2	$124.88	12.381%	$140.3414	$140.34	$140.35	$140.30
Purchase #3	$89.97	8.114%	$97.2702	$97.27	$97.25	$97.30
Purchase #4	$147.48	7.424%	$158.4289	$158.43	$158.45	$158.40
Purchase #5	$120.85	5.266%	$127.214	$127.21	$127.20	$127.20
Purchase #6	$111.44	10.646%	$123.3039	$123.30	$123.30	$123.30
Purchase #7	$213.27	5.312%	$224.5989	$224.60	$224.60	$224.60
7 purchase totals =	$916.73		$989.2814	$989.27	$989.25	$989.20