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	$115.98	6.402%	$123.405	$123.41	$123.40	$123.40
Purchase #2	$93.87	10.619%	$103.8381	$103.84	$103.85	$103.80
Purchase #3	$183.28	9.471%	$200.6384	$200.64	$200.65	$200.60
Purchase #4	$244.81	10.607%	$270.777	$270.78	$270.80	$270.80
Purchase #5	$48.37	9.792%	$53.1064	$53.11	$53.10	$53.10
Purchase #6	$19.97	12.454%	$22.4571	$22.46	$22.45	$22.50
Purchase #7	$219.62	10.457%	$242.5857	$242.59	$242.60	$242.60
7 purchase totals =	$925.90		$1,016.8077	$1,016.83	$1,016.85	$1,016.80