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	$22.41	13.625%	$25.4634	$25.46	$25.45	$25.50
Purchase #2	$97.29	11.843%	$108.8121	$108.81	$108.80	$108.80
Purchase #3	$100.64	10.719%	$111.4276	$111.43	$111.45	$111.40
Purchase #4	$27.95	12.422%	$31.4219	$31.42	$31.40	$31.40
Purchase #5	$109.58	3.588%	$113.5117	$113.51	$113.50	$113.50
Purchase #6	$141.25	3.710%	$146.4904	$146.49	$146.50	$146.50
Purchase #7	$122.26	8.319%	$132.4308	$132.43	$132.45	$132.40
7 purchase totals =	$621.38		$669.5579	$669.55	$669.55	$669.50