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	$32.93	7.852%	$35.5157	$35.52	$35.50	$35.50
Purchase #2	$132.31	12.188%	$148.4359	$148.44	$148.45	$148.40
Purchase #3	$171.70	7.642%	$184.8213	$184.82	$184.80	$184.80
Purchase #4	$136.96	5.524%	$144.5257	$144.53	$144.55	$144.50
Purchase #5	$30.57	4.213%	$31.8579	$31.86	$31.85	$31.90
Purchase #6	$142.74	10.544%	$157.7905	$157.79	$157.80	$157.80
Purchase #7	$38.64	11.554%	$43.1045	$43.10	$43.10	$43.10
7 purchase totals =	$685.85		$746.0515	$746.06	$746.05	$746.00