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	$199.99	13.262%	$226.5127	$226.51	$226.50	$226.50
Purchase #2	$83.51	7.632%	$89.8835	$89.88	$89.90	$89.90
Purchase #3	$232.74	6.705%	$248.3452	$248.35	$248.35	$248.30
Purchase #4	$100.60	3.226%	$103.8454	$103.85	$103.85	$103.80
Purchase #5	$223.73	12.454%	$251.5933	$251.59	$251.60	$251.60
Purchase #6	$61.90	5.105%	$65.06	$65.06	$65.05	$65.10
Purchase #7	$141.60	3.837%	$147.0332	$147.03	$147.05	$147.00
7 purchase totals =	$1,044.07		$1,132.2733	$1,132.27	$1,132.30	$1,132.20