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	$25.79	10.377%	$28.4662	$28.47	$28.45	$28.50
Purchase #2	$195.52	13.360%	$221.6415	$221.64	$221.65	$221.60
Purchase #3	$7.44	5.191%	$7.8262	$7.83	$7.85	$7.80
Purchase #4	$173.40	5.464%	$182.8746	$182.87	$182.85	$182.90
Purchase #5	$98.39	13.191%	$111.3686	$111.37	$111.35	$111.40
Purchase #6	$217.76	6.107%	$231.0586	$231.06	$231.05	$231.10
Purchase #7	$36.32	6.488%	$38.6764	$38.68	$38.70	$38.70
7 purchase totals =	$754.62		$821.9121	$821.92	$821.90	$822.00