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	$170.75	10.296%	$188.3304	$188.33	$188.35	$188.30
Purchase #2	$228.87	12.363%	$257.1652	$257.17	$257.15	$257.20
Purchase #3	$12.55	10.366%	$13.8509	$13.85	$13.85	$13.90
Purchase #4	$36.73	5.430%	$38.7244	$38.72	$38.70	$38.70
Purchase #5	$210.85	11.835%	$235.8041	$235.80	$235.80	$235.80
Purchase #6	$231.33	10.738%	$256.1702	$256.17	$256.15	$256.20
Purchase #7	$103.33	7.792%	$111.3815	$111.38	$111.40	$111.40
7 purchase totals =	$994.41		$1,101.4267	$1,101.42	$1,101.40	$1,101.50