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	$21.56	7.223%	$23.1173	$23.12	$23.10	$23.10
Purchase #2	$149.84	10.456%	$165.5073	$165.51	$165.50	$165.50
Purchase #3	$246.79	5.604%	$260.6201	$260.62	$260.60	$260.60
Purchase #4	$217.61	8.292%	$235.6542	$235.65	$235.65	$235.70
Purchase #5	$203.59	7.359%	$218.5722	$218.57	$218.55	$218.60
Purchase #6	$66.88	6.252%	$71.0613	$71.06	$71.05	$71.10
Purchase #7	$101.42	10.104%	$111.6675	$111.67	$111.65	$111.70
7 purchase totals =	$1,007.69		$1,086.1999	$1,086.20	$1,086.10	$1,086.30