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	$40.99	11.626%	$45.7555	$45.76	$45.75	$45.80
Purchase #2	$215.44	10.861%	$238.8389	$238.84	$238.85	$238.80
Purchase #3	$247.30	13.491%	$280.6632	$280.66	$280.65	$280.70
Purchase #4	$24.45	5.208%	$25.7234	$25.72	$25.70	$25.70
Purchase #5	$40.58	6.862%	$43.3646	$43.36	$43.35	$43.40
Purchase #6	$168.53	4.611%	$176.3009	$176.30	$176.30	$176.30
Purchase #7	$161.37	3.675%	$167.3003	$167.30	$167.30	$167.30
7 purchase totals =	$898.66		$977.9468	$977.94	$977.90	$978.00