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	$28.44	13.127%	$32.1733	$32.17	$32.15	$32.20
Purchase #2	$75.78	12.550%	$85.2904	$85.29	$85.30	$85.30
Purchase #3	$158.50	3.856%	$164.6118	$164.61	$164.60	$164.60
Purchase #4	$28.86	11.843%	$32.2779	$32.28	$32.30	$32.30
Purchase #5	$38.50	6.531%	$41.0144	$41.01	$41.00	$41.00
Purchase #6	$134.86	7.240%	$144.6239	$144.62	$144.60	$144.60
Purchase #7	$221.80	5.710%	$234.4648	$234.46	$234.45	$234.50
7 purchase totals =	$686.74		$734.4565	$734.44	$734.40	$734.50