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	$60.41	10.722%	$66.8872	$66.89	$66.90	$66.90
Purchase #2	$220.48	13.120%	$249.407	$249.41	$249.40	$249.40
Purchase #3	$215.47	12.684%	$242.8002	$242.80	$242.80	$242.80
Purchase #4	$106.87	5.370%	$112.6089	$112.61	$112.60	$112.60
Purchase #5	$205.26	9.636%	$225.0389	$225.04	$225.05	$225.00
Purchase #6	$153.47	11.451%	$171.0438	$171.04	$171.05	$171.00
Purchase #7	$65.87	9.535%	$72.1507	$72.15	$72.15	$72.20
7 purchase totals =	$1,027.83		$1,139.9367	$1,139.94	$1,139.95	$1,139.90