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	$70.56	11.529%	$78.6949	$78.69	$78.70	$78.70
Purchase #2	$13.26	6.553%	$14.1289	$14.13	$14.15	$14.10
Purchase #3	$7.30	10.379%	$8.0577	$8.06	$8.05	$8.10
Purchase #4	$14.28	12.468%	$16.0604	$16.06	$16.05	$16.10
Purchase #5	$128.77	8.176%	$139.2982	$139.30	$139.30	$139.30
Purchase #6	$116.45	13.139%	$131.7504	$131.75	$131.75	$131.80
Purchase #7	$32.44	7.459%	$34.8597	$34.86	$34.85	$34.90
7 purchase totals =	$383.06		$422.8502	$422.85	$422.85	$423.00