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	$135.62	6.300%	$144.1641	$144.16	$144.15	$144.20
Purchase #2	$136.28	6.519%	$145.1641	$145.16	$145.15	$145.20
Purchase #3	$156.75	10.750%	$173.6006	$173.60	$173.60	$173.60
Purchase #4	$139.98	7.389%	$150.3231	$150.32	$150.30	$150.30
Purchase #5	$183.79	4.156%	$191.4283	$191.43	$191.45	$191.40
Purchase #6	$221.53	12.537%	$249.3032	$249.30	$249.30	$249.30
Purchase #7	$133.61	4.277%	$139.3245	$139.32	$139.30	$139.30
7 purchase totals =	$1,107.56		$1,193.3079	$1,193.29	$1,193.25	$1,193.30