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	$84.91	5.764%	$89.8042	$89.80	$89.80	$89.80
Purchase #2	$40.83	9.305%	$44.6292	$44.63	$44.65	$44.60
Purchase #3	$13.33	10.525%	$14.733	$14.73	$14.75	$14.70
Purchase #4	$216.40	11.773%	$241.8768	$241.88	$241.90	$241.90
Purchase #5	$114.82	13.248%	$130.0314	$130.03	$130.05	$130.00
Purchase #6	$249.35	12.120%	$279.5712	$279.57	$279.55	$279.60
Purchase #7	$44.72	13.670%	$50.8332	$50.83	$50.85	$50.80
7 purchase totals =	$764.36		$851.4790	$851.47	$851.55	$851.40