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	$106.33	3.223%	$109.757	$109.76	$109.75	$109.80
Purchase #2	$107.31	4.219%	$111.8374	$111.84	$111.85	$111.80
Purchase #3	$120.26	4.509%	$125.6825	$125.68	$125.70	$125.70
Purchase #4	$12.37	9.846%	$13.588	$13.59	$13.60	$13.60
Purchase #5	$62.27	13.189%	$70.4828	$70.48	$70.50	$70.50
Purchase #6	$57.47	6.180%	$61.0216	$61.02	$61.00	$61.00
Purchase #7	$43.50	9.163%	$47.4859	$47.49	$47.50	$47.50
7 purchase totals =	$509.51		$539.8552	$539.86	$539.90	$539.90