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	$141.34	12.213%	$158.6019	$158.60	$158.60	$158.60
Purchase #2	$134.59	12.796%	$151.8121	$151.81	$151.80	$151.80
Purchase #3	$201.49	10.579%	$222.8056	$222.81	$222.80	$222.80
Purchase #4	$40.59	9.279%	$44.3563	$44.36	$44.35	$44.40
Purchase #5	$80.78	3.205%	$83.369	$83.37	$83.35	$83.40
Purchase #6	$183.82	10.683%	$203.4575	$203.46	$203.45	$203.50
Purchase #7	$100.39	3.406%	$103.8093	$103.81	$103.80	$103.80
7 purchase totals =	$883.00		$968.2117	$968.22	$968.15	$968.30