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	$203.88	12.348%	$229.0551	$229.06	$229.05	$229.10
Purchase #2	$105.55	13.382%	$119.6747	$119.67	$119.65	$119.70
Purchase #3	$149.84	7.239%	$160.6869	$160.69	$160.70	$160.70
Purchase #4	$29.79	11.745%	$33.2888	$33.29	$33.30	$33.30
Purchase #5	$213.58	3.702%	$221.4867	$221.49	$221.50	$221.50
Purchase #6	$178.60	10.269%	$196.9404	$196.94	$196.95	$196.90
Purchase #7	$137.60	10.236%	$151.6847	$151.68	$151.70	$151.70
7 purchase totals =	$1,018.84		$1,112.8173	$1,112.82	$1,112.85	$1,112.90