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	$158.77	7.180%	$170.1697	$170.17	$170.15	$170.20
Purchase #2	$57.41	7.521%	$61.7278	$61.73	$61.75	$61.70
Purchase #3	$225.41	6.565%	$240.2082	$240.21	$240.20	$240.20
Purchase #4	$90.37	11.295%	$100.5773	$100.58	$100.60	$100.60
Purchase #5	$224.45	13.702%	$255.2041	$255.20	$255.20	$255.20
Purchase #6	$222.55	12.193%	$249.6855	$249.69	$249.70	$249.70
Purchase #7	$29.79	8.316%	$32.2673	$32.27	$32.25	$32.30
7 purchase totals =	$1,008.75		$1,109.8399	$1,109.85	$1,109.85	$1,109.90