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	$144.36	10.584%	$159.6391	$159.64	$159.65	$159.60
Purchase #2	$84.90	6.381%	$90.3175	$90.32	$90.30	$90.30
Purchase #3	$169.62	5.168%	$178.386	$178.39	$178.40	$178.40
Purchase #4	$93.90	12.309%	$105.4582	$105.46	$105.45	$105.50
Purchase #5	$158.42	10.791%	$175.5151	$175.52	$175.50	$175.50
Purchase #6	$47.79	3.405%	$49.4172	$49.42	$49.40	$49.40
Purchase #7	$46.58	12.258%	$52.2898	$52.29	$52.30	$52.30
7 purchase totals =	$745.57		$811.0229	$811.04	$811.00	$811.00