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	$13.82	13.512%	$15.6874	$15.69	$15.70	$15.70
Purchase #2	$106.49	7.354%	$114.3213	$114.32	$114.30	$114.30
Purchase #3	$44.54	7.345%	$47.8115	$47.81	$47.80	$47.80
Purchase #4	$147.44	11.580%	$164.5136	$164.51	$164.50	$164.50
Purchase #5	$69.25	4.145%	$72.1204	$72.12	$72.10	$72.10
Purchase #6	$197.31	12.634%	$222.2381	$222.24	$222.25	$222.20
Purchase #7	$12.81	3.675%	$13.2808	$13.28	$13.30	$13.30
7 purchase totals =	$591.66		$649.9731	$649.97	$649.95	$649.90