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	$171.65	6.340%	$182.5326	$182.53	$182.55	$182.50
Purchase #2	$57.64	8.424%	$62.4956	$62.50	$62.50	$62.50
Purchase #3	$153.69	11.667%	$171.621	$171.62	$171.60	$171.60
Purchase #4	$121.96	10.134%	$134.3194	$134.32	$134.30	$134.30
Purchase #5	$190.89	9.317%	$208.6752	$208.68	$208.70	$208.70
Purchase #6	$47.82	13.298%	$54.1791	$54.18	$54.20	$54.20
Purchase #7	$158.61	5.253%	$166.9418	$166.94	$166.95	$166.90
7 purchase totals =	$902.26		$980.7647	$980.77	$980.80	$980.70