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	$123.58	6.408%	$131.499	$131.50	$131.50	$131.50
Purchase #2	$122.55	9.433%	$134.1101	$134.11	$134.10	$134.10
Purchase #3	$94.40	8.356%	$102.2881	$102.29	$102.30	$102.30
Purchase #4	$10.88	6.770%	$11.6166	$11.62	$11.60	$11.60
Purchase #5	$242.90	6.844%	$259.5241	$259.52	$259.50	$259.50
Purchase #6	$144.66	3.766%	$150.1079	$150.11	$150.10	$150.10
Purchase #7	$141.46	4.301%	$147.5442	$147.54	$147.55	$147.50
7 purchase totals =	$880.43		$936.6900	$936.69	$936.65	$936.60