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	$139.94	13.844%	$159.3133	$159.31	$159.30	$159.30
Purchase #2	$230.89	11.389%	$257.1861	$257.19	$257.20	$257.20
Purchase #3	$140.46	7.384%	$150.8316	$150.83	$150.85	$150.80
Purchase #4	$96.51	13.485%	$109.5244	$109.52	$109.50	$109.50
Purchase #5	$13.70	7.304%	$14.7006	$14.70	$14.70	$14.70
Purchase #6	$199.46	5.243%	$209.9177	$209.92	$209.90	$209.90
Purchase #7	$62.58	4.491%	$65.3905	$65.39	$65.40	$65.40
7 purchase totals =	$883.54		$966.8642	$966.86	$966.85	$966.80