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	$105.77	11.862%	$118.3164	$118.32	$118.30	$118.30
Purchase #2	$108.35	11.775%	$121.1082	$121.11	$121.10	$121.10
Purchase #3	$225.40	13.401%	$255.6059	$255.61	$255.60	$255.60
Purchase #4	$179.54	9.269%	$196.1816	$196.18	$196.20	$196.20
Purchase #5	$117.82	4.574%	$123.2091	$123.21	$123.20	$123.20
Purchase #6	$169.83	7.810%	$183.0937	$183.09	$183.10	$183.10
Purchase #7	$167.65	13.400%	$190.1151	$190.12	$190.10	$190.10
7 purchase totals =	$1,074.36		$1,187.6300	$1,187.64	$1,187.60	$1,187.60