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	$19.32	11.337%	$21.5103	$21.51	$21.50	$21.50
Purchase #2	$226.33	5.838%	$239.5431	$239.54	$239.55	$239.50
Purchase #3	$103.51	5.141%	$108.8314	$108.83	$108.85	$108.80
Purchase #4	$119.54	13.150%	$135.2595	$135.26	$135.25	$135.30
Purchase #5	$92.42	6.253%	$98.199	$98.20	$98.20	$98.20
Purchase #6	$96.67	4.223%	$100.7524	$100.75	$100.75	$100.80
Purchase #7	$78.92	13.252%	$89.3785	$89.38	$89.40	$89.40
7 purchase totals =	$736.71		$793.4742	$793.47	$793.50	$793.50