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	$95.60	5.346%	$100.7108	$100.71	$100.70	$100.70
Purchase #2	$204.78	10.250%	$225.77	$225.77	$225.75	$225.80
Purchase #3	$74.42	8.681%	$80.8804	$80.88	$80.90	$80.90
Purchase #4	$123.53	3.192%	$127.4731	$127.47	$127.45	$127.50
Purchase #5	$91.32	9.699%	$100.1771	$100.18	$100.20	$100.20
Purchase #6	$47.85	4.567%	$50.0353	$50.04	$50.05	$50.00
Purchase #7	$56.88	3.818%	$59.0517	$59.05	$59.05	$59.10
7 purchase totals =	$694.38		$744.0984	$744.10	$744.10	$744.20