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	$58.64	5.541%	$61.8892	$61.89	$61.90	$61.90
Purchase #2	$104.39	13.720%	$118.7123	$118.71	$118.70	$118.70
Purchase #3	$147.64	11.686%	$164.8932	$164.89	$164.90	$164.90
Purchase #4	$91.85	12.574%	$103.3992	$103.40	$103.40	$103.40
Purchase #5	$155.48	6.783%	$166.0262	$166.03	$166.05	$166.00
Purchase #6	$190.92	7.503%	$205.2447	$205.24	$205.25	$205.20
Purchase #7	$51.75	11.818%	$57.8658	$57.87	$57.85	$57.90
7 purchase totals =	$800.67		$878.0306	$878.03	$878.05	$878.00