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	$214.82	13.294%	$243.3782	$243.38	$243.40	$243.40
Purchase #2	$179.96	11.441%	$200.5492	$200.55	$200.55	$200.50
Purchase #3	$35.65	12.599%	$40.1415	$40.14	$40.15	$40.10
Purchase #4	$56.95	10.532%	$62.948	$62.95	$62.95	$62.90
Purchase #5	$130.94	7.452%	$140.6976	$140.70	$140.70	$140.70
Purchase #6	$123.85	3.718%	$128.4547	$128.45	$128.45	$128.50
Purchase #7	$148.28	3.471%	$153.4268	$153.43	$153.45	$153.40
7 purchase totals =	$890.45		$969.5960	$969.60	$969.65	$969.50