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	$158.90	4.211%	$165.5913	$165.59	$165.60	$165.60
Purchase #2	$161.40	6.191%	$171.3923	$171.39	$171.40	$171.40
Purchase #3	$78.49	10.732%	$86.9135	$86.91	$86.90	$86.90
Purchase #4	$50.95	3.475%	$52.7205	$52.72	$52.70	$52.70
Purchase #5	$73.43	12.462%	$82.5808	$82.58	$82.60	$82.60
Purchase #6	$47.82	6.516%	$50.936	$50.94	$50.95	$50.90
Purchase #7	$30.68	5.326%	$32.314	$32.31	$32.30	$32.30
7 purchase totals =	$601.67		$642.4484	$642.44	$642.45	$642.40