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	$239.59	4.103%	$249.4204	$249.42	$249.40	$249.40
Purchase #2	$166.45	7.738%	$179.3299	$179.33	$179.35	$179.30
Purchase #3	$64.86	9.803%	$71.2182	$71.22	$71.20	$71.20
Purchase #4	$179.69	9.371%	$196.5287	$196.53	$196.55	$196.50
Purchase #5	$204.97	3.194%	$211.5167	$211.52	$211.50	$211.50
Purchase #6	$97.71	5.519%	$103.1026	$103.10	$103.10	$103.10
Purchase #7	$136.31	6.777%	$145.5477	$145.55	$145.55	$145.50
7 purchase totals =	$1,089.58		$1,156.6642	$1,156.67	$1,156.65	$1,156.50