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	$37.28	13.337%	$42.252	$42.25	$42.25	$42.30
Purchase #2	$109.79	3.273%	$113.3834	$113.38	$113.40	$113.40
Purchase #3	$28.37	10.322%	$31.2984	$31.30	$31.30	$31.30
Purchase #4	$245.62	4.238%	$256.0294	$256.03	$256.05	$256.00
Purchase #5	$184.44	11.443%	$205.5455	$205.55	$205.55	$205.50
Purchase #6	$159.81	8.303%	$173.079	$173.08	$173.10	$173.10
Purchase #7	$151.49	3.388%	$156.6225	$156.62	$156.60	$156.60
7 purchase totals =	$916.80		$978.2102	$978.21	$978.25	$978.20