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	$47.61	12.268%	$53.4508	$53.45	$53.45	$53.50
Purchase #2	$13.88	10.729%	$15.3692	$15.37	$15.35	$15.40
Purchase #3	$147.49	3.205%	$152.2171	$152.22	$152.20	$152.20
Purchase #4	$75.43	9.862%	$82.8689	$82.87	$82.85	$82.90
Purchase #5	$248.58	12.653%	$280.0328	$280.03	$280.05	$280.00
Purchase #6	$50.87	9.467%	$55.6859	$55.69	$55.70	$55.70
Purchase #7	$49.47	8.512%	$53.6809	$53.68	$53.70	$53.70
7 purchase totals =	$633.33		$693.3056	$693.31	$693.30	$693.40