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	$244.81	8.257%	$265.024	$265.02	$265.00	$265.00
Purchase #2	$104.89	4.568%	$109.6814	$109.68	$109.70	$109.70
Purchase #3	$139.75	9.439%	$152.941	$152.94	$152.95	$152.90
Purchase #4	$150.35	3.652%	$155.8408	$155.84	$155.85	$155.80
Purchase #5	$49.36	7.767%	$53.1938	$53.19	$53.20	$53.20
Purchase #6	$43.47	4.772%	$45.5444	$45.54	$45.55	$45.50
Purchase #7	$45.71	5.641%	$48.2885	$48.29	$48.30	$48.30
7 purchase totals =	$778.34		$830.5139	$830.50	$830.55	$830.40