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	$72.88	12.208%	$81.7772	$81.78	$81.80	$81.80
Purchase #2	$44.89	13.467%	$50.9353	$50.94	$50.95	$50.90
Purchase #3	$128.51	7.338%	$137.9401	$137.94	$137.95	$137.90
Purchase #4	$69.51	12.596%	$78.2655	$78.27	$78.25	$78.30
Purchase #5	$53.68	10.298%	$59.208	$59.21	$59.20	$59.20
Purchase #6	$208.41	10.677%	$230.6619	$230.66	$230.65	$230.70
Purchase #7	$51.44	5.350%	$54.192	$54.19	$54.20	$54.20
7 purchase totals =	$629.32		$692.9800	$692.99	$693.00	$693.00