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	$108.52	3.869%	$112.7186	$112.72	$112.70	$112.70
Purchase #2	$135.93	12.320%	$152.6766	$152.68	$152.70	$152.70
Purchase #3	$82.95	11.240%	$92.2736	$92.27	$92.25	$92.30
Purchase #4	$220.56	6.821%	$235.6044	$235.60	$235.60	$235.60
Purchase #5	$229.49	11.755%	$256.4665	$256.47	$256.45	$256.50
Purchase #6	$62.82	12.410%	$70.616	$70.62	$70.60	$70.60
Purchase #7	$52.68	12.125%	$59.0675	$59.07	$59.05	$59.10
7 purchase totals =	$892.95		$979.4232	$979.43	$979.35	$979.50