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	$46.96	8.371%	$50.891	$50.89	$50.90	$50.90
Purchase #2	$10.47	13.612%	$11.8952	$11.90	$11.90	$11.90
Purchase #3	$134.30	6.405%	$142.9019	$142.90	$142.90	$142.90
Purchase #4	$116.72	9.236%	$127.5003	$127.50	$127.50	$127.50
Purchase #5	$165.49	11.290%	$184.1738	$184.17	$184.15	$184.20
Purchase #6	$227.48	4.522%	$237.7666	$237.77	$237.75	$237.80
Purchase #7	$102.27	7.338%	$109.7746	$109.77	$109.75	$109.80
7 purchase totals =	$803.69		$864.9034	$864.90	$864.85	$865.00