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	$44.27	13.638%	$50.3075	$50.31	$50.30	$50.30
Purchase #2	$178.45	10.616%	$197.3943	$197.39	$197.40	$197.40
Purchase #3	$73.52	6.372%	$78.2047	$78.20	$78.20	$78.20
Purchase #4	$55.82	6.373%	$59.3774	$59.38	$59.40	$59.40
Purchase #5	$190.73	3.485%	$197.3769	$197.38	$197.40	$197.40
Purchase #6	$101.54	5.257%	$106.878	$106.88	$106.90	$106.90
Purchase #7	$66.52	8.763%	$72.3491	$72.35	$72.35	$72.30
7 purchase totals =	$710.85		$761.8879	$761.89	$761.95	$761.90