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	$11.96	5.357%	$12.6007	$12.60	$12.60	$12.60
Purchase #2	$228.77	6.805%	$244.3378	$244.34	$244.35	$244.30
Purchase #3	$236.55	10.801%	$262.0998	$262.10	$262.10	$262.10
Purchase #4	$124.79	4.712%	$130.6701	$130.67	$130.65	$130.70
Purchase #5	$147.62	12.655%	$166.3013	$166.30	$166.30	$166.30
Purchase #6	$83.28	7.137%	$89.2237	$89.22	$89.20	$89.20
Purchase #7	$160.92	9.820%	$176.7223	$176.72	$176.70	$176.70
7 purchase totals =	$993.89		$1,081.9557	$1,081.95	$1,081.90	$1,081.90