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	$202.71	13.308%	$229.6866	$229.69	$229.70	$229.70
Purchase #2	$176.40	5.193%	$185.5605	$185.56	$185.55	$185.60
Purchase #3	$64.53	4.655%	$67.5339	$67.53	$67.55	$67.50
Purchase #4	$115.93	6.609%	$123.5918	$123.59	$123.60	$123.60
Purchase #5	$57.29	3.451%	$59.2671	$59.27	$59.25	$59.30
Purchase #6	$160.73	5.188%	$169.0687	$169.07	$169.05	$169.10
Purchase #7	$129.52	9.713%	$142.1003	$142.10	$142.10	$142.10
7 purchase totals =	$907.11		$976.8089	$976.81	$976.80	$976.90