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	$9.40	10.388%	$10.3765	$10.38	$10.40	$10.40
Purchase #2	$178.27	10.868%	$197.6444	$197.64	$197.65	$197.60
Purchase #3	$137.26	9.323%	$150.0567	$150.06	$150.05	$150.10
Purchase #4	$139.62	8.203%	$151.073	$151.07	$151.05	$151.10
Purchase #5	$150.70	9.724%	$165.3541	$165.35	$165.35	$165.40
Purchase #6	$108.32	4.334%	$113.0146	$113.01	$113.00	$113.00
Purchase #7	$200.73	7.537%	$215.859	$215.86	$215.85	$215.90
7 purchase totals =	$924.30		$1,003.3783	$1,003.37	$1,003.35	$1,003.50