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	$136.31	10.397%	$150.4822	$150.48	$150.50	$150.50
Purchase #2	$169.33	12.800%	$191.0042	$191.00	$191.00	$191.00
Purchase #3	$132.91	8.647%	$144.4027	$144.40	$144.40	$144.40
Purchase #4	$20.29	11.369%	$22.5968	$22.60	$22.60	$22.60
Purchase #5	$123.43	9.233%	$134.8263	$134.83	$134.85	$134.80
Purchase #6	$141.50	9.842%	$155.4264	$155.43	$155.45	$155.40
Purchase #7	$134.83	5.139%	$141.7589	$141.76	$141.75	$141.80
7 purchase totals =	$858.60		$940.4975	$940.50	$940.55	$940.50