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	$90.49	8.438%	$98.1255	$98.13	$98.15	$98.10
Purchase #2	$97.43	3.155%	$100.5039	$100.50	$100.50	$100.50
Purchase #3	$34.55	11.680%	$38.5854	$38.59	$38.60	$38.60
Purchase #4	$187.91	13.519%	$213.3136	$213.31	$213.30	$213.30
Purchase #5	$42.55	11.376%	$47.3905	$47.39	$47.40	$47.40
Purchase #6	$166.43	9.758%	$182.6702	$182.67	$182.65	$182.70
Purchase #7	$228.28	13.152%	$258.3034	$258.30	$258.30	$258.30
7 purchase totals =	$847.64		$938.8925	$938.89	$938.90	$938.90