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	$107.29	7.536%	$115.3754	$115.38	$115.40	$115.40
Purchase #2	$63.71	13.602%	$72.3758	$72.38	$72.40	$72.40
Purchase #3	$50.77	11.450%	$56.5832	$56.58	$56.60	$56.60
Purchase #4	$55.72	6.244%	$59.1992	$59.20	$59.20	$59.20
Purchase #5	$228.31	10.218%	$251.6387	$251.64	$251.65	$251.60
Purchase #6	$36.35	9.829%	$39.9228	$39.92	$39.90	$39.90
Purchase #7	$78.65	12.185%	$88.2335	$88.23	$88.25	$88.20
7 purchase totals =	$620.80		$683.3286	$683.33	$683.40	$683.30