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	$71.43	12.647%	$80.4638	$80.46	$80.45	$80.50
Purchase #2	$157.33	7.174%	$168.6169	$168.62	$168.60	$168.60
Purchase #3	$247.89	6.723%	$264.5556	$264.56	$264.55	$264.60
Purchase #4	$188.44	13.768%	$214.3844	$214.38	$214.40	$214.40
Purchase #5	$80.75	11.823%	$90.2971	$90.30	$90.30	$90.30
Purchase #6	$128.97	9.181%	$140.8107	$140.81	$140.80	$140.80
Purchase #7	$128.81	4.767%	$134.9504	$134.95	$134.95	$135.00
7 purchase totals =	$1,003.62		$1,094.0789	$1,094.08	$1,094.05	$1,094.20