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	$127.56	6.697%	$136.1027	$136.10	$136.10	$136.10
Purchase #2	$186.25	4.367%	$194.3835	$194.38	$194.40	$194.40
Purchase #3	$183.46	12.186%	$205.8164	$205.82	$205.80	$205.80
Purchase #4	$225.51	5.574%	$238.0799	$238.08	$238.10	$238.10
Purchase #5	$23.87	13.372%	$27.0619	$27.06	$27.05	$27.10
Purchase #6	$90.33	9.730%	$99.1191	$99.12	$99.10	$99.10
Purchase #7	$119.35	9.492%	$130.6787	$130.68	$130.70	$130.70
7 purchase totals =	$956.33		$1,031.2422	$1,031.24	$1,031.25	$1,031.30