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	$35.37	9.103%	$38.5897	$38.59	$38.60	$38.60
Purchase #2	$41.42	5.747%	$43.8004	$43.80	$43.80	$43.80
Purchase #3	$79.71	12.812%	$89.9224	$89.92	$89.90	$89.90
Purchase #4	$12.69	7.754%	$13.674	$13.67	$13.65	$13.70
Purchase #5	$174.40	4.272%	$181.8504	$181.85	$181.85	$181.90
Purchase #6	$129.72	4.327%	$135.333	$135.33	$135.35	$135.30
Purchase #7	$142.83	9.485%	$156.3774	$156.38	$156.40	$156.40
7 purchase totals =	$616.14		$659.5473	$659.54	$659.55	$659.60