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	$70.28	11.707%	$78.5077	$78.51	$78.50	$78.50
Purchase #2	$62.68	4.135%	$65.2718	$65.27	$65.25	$65.30
Purchase #3	$186.47	5.395%	$196.5301	$196.53	$196.55	$196.50
Purchase #4	$21.37	9.183%	$23.3324	$23.33	$23.35	$23.30
Purchase #5	$241.59	9.544%	$264.6473	$264.65	$264.65	$264.60
Purchase #6	$234.70	6.549%	$250.0705	$250.07	$250.05	$250.10
Purchase #7	$183.63	7.153%	$196.7651	$196.77	$196.75	$196.80
7 purchase totals =	$1,000.72		$1,075.1249	$1,075.13	$1,075.10	$1,075.10