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	$250.37	13.248%	$283.539	$283.54	$283.55	$283.50
Purchase #2	$99.68	6.752%	$106.4104	$106.41	$106.40	$106.40
Purchase #3	$198.34	11.682%	$221.5101	$221.51	$221.50	$221.50
Purchase #4	$190.50	3.178%	$196.5541	$196.55	$196.55	$196.60
Purchase #5	$108.42	7.307%	$116.3422	$116.34	$116.35	$116.30
Purchase #6	$117.92	9.614%	$129.2568	$129.26	$129.25	$129.30
Purchase #7	$84.78	5.441%	$89.3929	$89.39	$89.40	$89.40
7 purchase totals =	$1,050.01		$1,143.0055	$1,143.00	$1,143.00	$1,143.00