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	$28.56	3.627%	$29.5959	$29.60	$29.60	$29.60
Purchase #2	$249.54	8.797%	$271.492	$271.49	$271.50	$271.50
Purchase #3	$243.76	4.564%	$254.8852	$254.89	$254.90	$254.90
Purchase #4	$246.45	12.820%	$278.0449	$278.04	$278.05	$278.00
Purchase #5	$104.32	5.817%	$110.3883	$110.39	$110.40	$110.40
Purchase #6	$25.63	13.255%	$29.0273	$29.03	$29.05	$29.00
Purchase #7	$172.28	9.761%	$189.0963	$189.10	$189.10	$189.10
7 purchase totals =	$1,070.54		$1,162.5299	$1,162.54	$1,162.60	$1,162.50