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	$241.53	12.511%	$271.7478	$271.75	$271.75	$271.70
Purchase #2	$150.79	13.799%	$171.5975	$171.60	$171.60	$171.60
Purchase #3	$224.92	13.851%	$256.0737	$256.07	$256.05	$256.10
Purchase #4	$222.56	9.790%	$244.3486	$244.35	$244.35	$244.30
Purchase #5	$46.65	4.407%	$48.7059	$48.71	$48.70	$48.70
Purchase #6	$99.55	3.588%	$103.1219	$103.12	$103.10	$103.10
Purchase #7	$99.97	5.297%	$105.2654	$105.27	$105.25	$105.30
7 purchase totals =	$1,085.97		$1,200.8608	$1,200.87	$1,200.80	$1,200.80