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	$188.85	5.737%	$199.6843	$199.68	$199.70	$199.70
Purchase #2	$104.28	7.217%	$111.8059	$111.81	$111.80	$111.80
Purchase #3	$41.45	3.744%	$43.0019	$43.00	$43.00	$43.00
Purchase #4	$202.79	10.724%	$224.5372	$224.54	$224.55	$224.50
Purchase #5	$123.56	12.123%	$138.5392	$138.54	$138.55	$138.50
Purchase #6	$106.89	12.644%	$120.4052	$120.41	$120.40	$120.40
Purchase #7	$38.82	9.246%	$42.4093	$42.41	$42.40	$42.40
7 purchase totals =	$806.64		$880.3830	$880.39	$880.40	$880.30