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	$238.37	13.872%	$271.4367	$271.44	$271.45	$271.40
Purchase #2	$118.61	7.214%	$127.1665	$127.17	$127.15	$127.20
Purchase #3	$109.54	3.463%	$113.3334	$113.33	$113.35	$113.30
Purchase #4	$217.55	5.225%	$228.917	$228.92	$228.90	$228.90
Purchase #5	$64.58	11.531%	$72.0267	$72.03	$72.05	$72.00
Purchase #6	$104.62	6.593%	$111.5176	$111.52	$111.50	$111.50
Purchase #7	$45.66	8.846%	$49.6991	$49.70	$49.70	$49.70
7 purchase totals =	$898.93		$974.0970	$974.11	$974.10	$974.00