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	$89.68	11.631%	$100.1107	$100.11	$100.10	$100.10
Purchase #2	$214.74	11.618%	$239.6885	$239.69	$239.70	$239.70
Purchase #3	$201.32	6.494%	$214.3937	$214.39	$214.40	$214.40
Purchase #4	$29.90	5.732%	$31.6139	$31.61	$31.60	$31.60
Purchase #5	$111.85	5.870%	$118.4156	$118.42	$118.40	$118.40
Purchase #6	$142.74	11.186%	$158.7069	$158.71	$158.70	$158.70
Purchase #7	$163.62	13.133%	$185.1082	$185.11	$185.10	$185.10
7 purchase totals =	$953.85		$1,048.0375	$1,048.04	$1,048.00	$1,048.00