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	$18.32	12.293%	$20.5721	$20.57	$20.55	$20.60
Purchase #2	$104.73	6.392%	$111.4243	$111.42	$111.40	$111.40
Purchase #3	$75.77	12.180%	$84.9988	$85.00	$85.00	$85.00
Purchase #4	$111.76	4.173%	$116.4237	$116.42	$116.40	$116.40
Purchase #5	$176.86	4.265%	$184.4031	$184.40	$184.40	$184.40
Purchase #6	$189.47	11.409%	$211.0866	$211.09	$211.10	$211.10
Purchase #7	$164.45	11.507%	$183.3733	$183.37	$183.35	$183.40
7 purchase totals =	$841.36		$912.2819	$912.27	$912.20	$912.30