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	$52.53	12.308%	$58.9954	$59.00	$59.00	$59.00
Purchase #2	$135.52	13.851%	$154.2909	$154.29	$154.30	$154.30
Purchase #3	$142.43	6.708%	$151.9842	$151.98	$152.00	$152.00
Purchase #4	$21.79	5.342%	$22.954	$22.95	$22.95	$23.00
Purchase #5	$51.39	8.387%	$55.7001	$55.70	$55.70	$55.70
Purchase #6	$57.40	7.361%	$61.6252	$61.63	$61.65	$61.60
Purchase #7	$12.65	9.832%	$13.8937	$13.89	$13.90	$13.90
7 purchase totals =	$473.71		$519.4435	$519.44	$519.50	$519.50