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	$127.51	7.367%	$136.9037	$136.90	$136.90	$136.90
Purchase #2	$218.90	12.451%	$246.1552	$246.16	$246.15	$246.20
Purchase #3	$191.99	6.724%	$204.8994	$204.90	$204.90	$204.90
Purchase #4	$147.71	9.742%	$162.0999	$162.10	$162.10	$162.10
Purchase #5	$25.34	7.364%	$27.206	$27.21	$27.20	$27.20
Purchase #6	$103.28	5.401%	$108.8582	$108.86	$108.85	$108.90
Purchase #7	$104.85	6.316%	$111.4723	$111.47	$111.45	$111.50
7 purchase totals =	$919.58		$997.5947	$997.60	$997.55	$997.70