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	$129.31	11.839%	$144.619	$144.62	$144.60	$144.60
Purchase #2	$38.88	10.351%	$42.9045	$42.90	$42.90	$42.90
Purchase #3	$241.33	8.399%	$261.5993	$261.60	$261.60	$261.60
Purchase #4	$231.86	8.752%	$252.1524	$252.15	$252.15	$252.20
Purchase #5	$197.86	7.589%	$212.8756	$212.88	$212.90	$212.90
Purchase #6	$96.43	13.533%	$109.4799	$109.48	$109.50	$109.50
Purchase #7	$162.65	6.851%	$173.7932	$173.79	$173.80	$173.80
7 purchase totals =	$1,098.32		$1,197.4239	$1,197.42	$1,197.45	$1,197.50