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	$171.61	6.527%	$182.811	$182.81	$182.80	$182.80
Purchase #2	$140.68	12.600%	$158.4057	$158.41	$158.40	$158.40
Purchase #3	$47.32	12.689%	$53.3244	$53.32	$53.30	$53.30
Purchase #4	$7.30	13.691%	$8.2994	$8.30	$8.30	$8.30
Purchase #5	$103.68	7.680%	$111.6426	$111.64	$111.65	$111.60
Purchase #6	$162.79	11.361%	$181.2846	$181.28	$181.30	$181.30
Purchase #7	$226.54	12.808%	$255.5552	$255.56	$255.55	$255.60
7 purchase totals =	$859.92		$951.3229	$951.32	$951.30	$951.30