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	$127.72	9.144%	$139.3987	$139.40	$139.40	$139.40
Purchase #2	$132.94	6.866%	$142.0677	$142.07	$142.05	$142.10
Purchase #3	$204.72	10.650%	$226.5227	$226.52	$226.50	$226.50
Purchase #4	$39.25	11.184%	$43.6397	$43.64	$43.65	$43.60
Purchase #5	$22.36	7.137%	$23.9558	$23.96	$23.95	$24.00
Purchase #6	$57.46	12.743%	$64.7821	$64.78	$64.80	$64.80
Purchase #7	$80.88	10.306%	$89.2155	$89.22	$89.20	$89.20
7 purchase totals =	$665.33		$729.5822	$729.59	$729.55	$729.60