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	$47.86	12.109%	$53.6554	$53.66	$53.65	$53.70
Purchase #2	$138.82	12.407%	$156.0434	$156.04	$156.05	$156.00
Purchase #3	$25.31	13.300%	$28.6762	$28.68	$28.70	$28.70
Purchase #4	$99.76	13.348%	$113.076	$113.08	$113.10	$113.10
Purchase #5	$56.70	13.488%	$64.3477	$64.35	$64.35	$64.30
Purchase #6	$99.35	4.109%	$103.4323	$103.43	$103.45	$103.40
Purchase #7	$83.81	5.408%	$88.3424	$88.34	$88.35	$88.30
7 purchase totals =	$551.61		$607.5734	$607.58	$607.65	$607.50