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	$203.76	13.627%	$231.5264	$231.53	$231.55	$231.50
Purchase #2	$78.58	8.212%	$85.033	$85.03	$85.05	$85.00
Purchase #3	$131.61	8.714%	$143.0785	$143.08	$143.10	$143.10
Purchase #4	$179.69	9.620%	$196.9762	$196.98	$197.00	$197.00
Purchase #5	$57.70	6.213%	$61.2849	$61.28	$61.30	$61.30
Purchase #6	$35.62	11.128%	$39.5838	$39.58	$39.60	$39.60
Purchase #7	$62.38	4.693%	$65.3075	$65.31	$65.30	$65.30
7 purchase totals =	$749.34		$822.7903	$822.79	$822.90	$822.80