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	$185.74	7.763%	$200.159	$200.16	$200.15	$200.20
Purchase #2	$106.31	12.146%	$119.2224	$119.22	$119.20	$119.20
Purchase #3	$156.27	6.839%	$166.9573	$166.96	$166.95	$167.00
Purchase #4	$100.33	12.274%	$112.6445	$112.64	$112.65	$112.60
Purchase #5	$202.80	8.220%	$219.4702	$219.47	$219.45	$219.50
Purchase #6	$156.27	7.421%	$167.8668	$167.87	$167.85	$167.90
Purchase #7	$11.78	7.713%	$12.6886	$12.69	$12.70	$12.70
7 purchase totals =	$919.50		$999.0088	$999.01	$998.95	$999.10