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	$71.85	10.682%	$79.525	$79.53	$79.55	$79.50
Purchase #2	$46.91	7.333%	$50.3499	$50.35	$50.35	$50.30
Purchase #3	$164.85	12.691%	$185.7711	$185.77	$185.75	$185.80
Purchase #4	$22.25	5.717%	$23.522	$23.52	$23.50	$23.50
Purchase #5	$36.81	9.501%	$40.3073	$40.31	$40.30	$40.30
Purchase #6	$153.79	10.748%	$170.3193	$170.32	$170.30	$170.30
Purchase #7	$148.77	10.850%	$164.9115	$164.91	$164.90	$164.90
7 purchase totals =	$645.23		$714.7061	$714.71	$714.65	$714.60