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	$157.28	7.726%	$169.4315	$169.43	$169.45	$169.40
Purchase #2	$142.86	11.655%	$159.5103	$159.51	$159.50	$159.50
Purchase #3	$108.86	10.208%	$119.9724	$119.97	$119.95	$120.00
Purchase #4	$73.63	6.616%	$78.5014	$78.50	$78.50	$78.50
Purchase #5	$18.79	11.484%	$20.9478	$20.95	$20.95	$20.90
Purchase #6	$63.62	4.115%	$66.238	$66.24	$66.25	$66.20
Purchase #7	$38.91	8.146%	$42.0796	$42.08	$42.10	$42.10
7 purchase totals =	$603.95		$656.6810	$656.68	$656.70	$656.60