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	$89.64	9.794%	$98.4193	$98.42	$98.40	$98.40
Purchase #2	$69.45	6.259%	$73.7969	$73.80	$73.80	$73.80
Purchase #3	$165.84	8.485%	$179.9115	$179.91	$179.90	$179.90
Purchase #4	$225.82	6.862%	$241.3158	$241.32	$241.30	$241.30
Purchase #5	$47.29	12.375%	$53.1421	$53.14	$53.15	$53.10
Purchase #6	$187.37	9.849%	$205.8241	$205.82	$205.80	$205.80
Purchase #7	$33.71	13.524%	$38.2689	$38.27	$38.25	$38.30
7 purchase totals =	$819.12		$890.6786	$890.68	$890.60	$890.60