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	$154.41	12.329%	$173.4472	$173.45	$173.45	$173.40
Purchase #2	$228.75	5.299%	$240.8715	$240.87	$240.85	$240.90
Purchase #3	$211.31	6.668%	$225.4002	$225.40	$225.40	$225.40
Purchase #4	$128.80	13.857%	$146.6478	$146.65	$146.65	$146.60
Purchase #5	$120.55	6.854%	$128.8125	$128.81	$128.80	$128.80
Purchase #6	$241.70	6.135%	$256.5283	$256.53	$256.55	$256.50
Purchase #7	$80.59	3.409%	$83.3373	$83.34	$83.35	$83.30
7 purchase totals =	$1,166.11		$1,255.0448	$1,255.05	$1,255.05	$1,254.90