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	$102.59	10.449%	$113.3096	$113.31	$113.30	$113.30
Purchase #2	$183.71	13.392%	$208.3124	$208.31	$208.30	$208.30
Purchase #3	$150.86	10.233%	$166.2975	$166.30	$166.30	$166.30
Purchase #4	$48.73	6.501%	$51.8979	$51.90	$51.90	$51.90
Purchase #5	$193.87	13.209%	$219.4783	$219.48	$219.50	$219.50
Purchase #6	$49.30	13.532%	$55.9713	$55.97	$55.95	$56.00
Purchase #7	$38.98	12.408%	$43.8166	$43.82	$43.80	$43.80
7 purchase totals =	$768.04		$859.0836	$859.09	$859.05	$859.10