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	$136.71	5.397%	$144.0882	$144.09	$144.10	$144.10
Purchase #2	$235.43	7.170%	$252.3103	$252.31	$252.30	$252.30
Purchase #3	$231.51	12.558%	$260.583	$260.58	$260.60	$260.60
Purchase #4	$80.69	13.485%	$91.571	$91.57	$91.55	$91.60
Purchase #5	$102.60	11.628%	$114.5303	$114.53	$114.55	$114.50
Purchase #6	$116.26	9.374%	$127.1582	$127.16	$127.15	$127.20
Purchase #7	$150.45	11.148%	$167.2222	$167.22	$167.20	$167.20
7 purchase totals =	$1,053.65		$1,157.4632	$1,157.46	$1,157.45	$1,157.50