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	$77.54	7.105%	$83.0492	$83.05	$83.05	$83.00
Purchase #2	$35.67	11.371%	$39.726	$39.73	$39.75	$39.70
Purchase #3	$77.67	11.549%	$86.6401	$86.64	$86.65	$86.60
Purchase #4	$175.67	5.295%	$184.9717	$184.97	$184.95	$185.00
Purchase #5	$17.86	12.665%	$20.122	$20.12	$20.10	$20.10
Purchase #6	$33.85	13.525%	$38.4282	$38.43	$38.45	$38.40
Purchase #7	$46.65	9.477%	$51.071	$51.07	$51.05	$51.10
7 purchase totals =	$464.91		$504.0082	$504.01	$504.00	$503.90