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	$144.88	11.199%	$161.1051	$161.11	$161.10	$161.10
Purchase #2	$146.95	3.856%	$152.6164	$152.62	$152.60	$152.60
Purchase #3	$198.54	11.469%	$221.3106	$221.31	$221.30	$221.30
Purchase #4	$70.91	13.795%	$80.692	$80.69	$80.70	$80.70
Purchase #5	$136.57	5.514%	$144.1005	$144.10	$144.10	$144.10
Purchase #6	$41.54	5.495%	$43.8226	$43.82	$43.80	$43.80
Purchase #7	$152.71	9.119%	$166.6356	$166.64	$166.65	$166.60
7 purchase totals =	$892.10		$970.2828	$970.29	$970.25	$970.20