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	$17.75	3.613%	$18.3913	$18.39	$18.40	$18.40
Purchase #2	$250.48	13.648%	$284.6655	$284.67	$284.65	$284.70
Purchase #3	$105.32	10.333%	$116.2027	$116.20	$116.20	$116.20
Purchase #4	$12.45	13.600%	$14.1432	$14.14	$14.15	$14.10
Purchase #5	$51.29	4.524%	$53.6104	$53.61	$53.60	$53.60
Purchase #6	$130.26	6.806%	$139.1255	$139.13	$139.15	$139.10
Purchase #7	$181.67	8.112%	$196.4071	$196.41	$196.40	$196.40
7 purchase totals =	$749.22		$822.5457	$822.55	$822.55	$822.50