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	$54.94	8.247%	$59.4709	$59.47	$59.45	$59.50
Purchase #2	$106.51	3.486%	$110.2229	$110.22	$110.20	$110.20
Purchase #3	$25.70	10.564%	$28.4149	$28.41	$28.40	$28.40
Purchase #4	$134.57	6.828%	$143.7584	$143.76	$143.75	$143.80
Purchase #5	$104.46	4.444%	$109.1022	$109.10	$109.10	$109.10
Purchase #6	$91.57	12.661%	$103.1637	$103.16	$103.15	$103.20
Purchase #7	$50.33	8.239%	$54.4767	$54.48	$54.50	$54.50
7 purchase totals =	$568.08		$608.6097	$608.60	$608.55	$608.70