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	$126.59	12.727%	$142.7011	$142.70	$142.70	$142.70
Purchase #2	$213.26	9.861%	$234.2896	$234.29	$234.30	$234.30
Purchase #3	$39.97	11.517%	$44.5733	$44.57	$44.55	$44.60
Purchase #4	$16.52	9.629%	$18.1107	$18.11	$18.10	$18.10
Purchase #5	$50.32	5.207%	$52.9402	$52.94	$52.95	$52.90
Purchase #6	$47.38	12.859%	$53.4726	$53.47	$53.45	$53.50
Purchase #7	$40.72	10.566%	$45.0225	$45.02	$45.00	$45.00
7 purchase totals =	$534.76		$591.1100	$591.10	$591.05	$591.10