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	$154.92	12.773%	$174.7079	$174.71	$174.70	$174.70
Purchase #2	$241.53	12.447%	$271.5932	$271.59	$271.60	$271.60
Purchase #3	$46.41	4.476%	$48.4873	$48.49	$48.50	$48.50
Purchase #4	$74.46	11.515%	$83.0341	$83.03	$83.05	$83.00
Purchase #5	$106.37	4.808%	$111.4843	$111.48	$111.50	$111.50
Purchase #6	$13.72	7.783%	$14.7878	$14.79	$14.80	$14.80
Purchase #7	$127.44	6.225%	$135.3731	$135.37	$135.35	$135.40
7 purchase totals =	$764.85		$839.4677	$839.46	$839.50	$839.50