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	$151.82	12.450%	$170.7216	$170.72	$170.70	$170.70
Purchase #2	$108.73	13.281%	$123.1704	$123.17	$123.15	$123.20
Purchase #3	$72.90	13.273%	$82.576	$82.58	$82.60	$82.60
Purchase #4	$19.92	9.638%	$21.8399	$21.84	$21.85	$21.80
Purchase #5	$62.65	10.233%	$69.061	$69.06	$69.05	$69.10
Purchase #6	$210.91	3.539%	$218.3741	$218.37	$218.35	$218.40
Purchase #7	$127.89	12.389%	$143.7343	$143.73	$143.75	$143.70
7 purchase totals =	$754.82		$829.4773	$829.47	$829.45	$829.50