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	$51.90	8.491%	$56.3068	$56.31	$56.30	$56.30
Purchase #2	$54.69	3.194%	$56.4368	$56.44	$56.45	$56.40
Purchase #3	$193.33	13.330%	$219.1009	$219.10	$219.10	$219.10
Purchase #4	$179.71	9.534%	$196.8436	$196.84	$196.85	$196.80
Purchase #5	$174.49	7.128%	$186.9276	$186.93	$186.95	$186.90
Purchase #6	$137.37	10.136%	$151.2938	$151.29	$151.30	$151.30
Purchase #7	$79.30	12.688%	$89.3616	$89.36	$89.35	$89.40
7 purchase totals =	$870.79		$956.2711	$956.27	$956.30	$956.20