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	$90.65	11.211%	$100.8128	$100.81	$100.80	$100.80
Purchase #2	$123.42	4.556%	$129.043	$129.04	$129.05	$129.00
Purchase #3	$140.61	11.559%	$156.8631	$156.86	$156.85	$156.90
Purchase #4	$227.31	4.704%	$238.0027	$238.00	$238.00	$238.00
Purchase #5	$110.25	9.107%	$120.2905	$120.29	$120.30	$120.30
Purchase #6	$41.76	12.773%	$47.094	$47.09	$47.10	$47.10
Purchase #7	$153.82	3.611%	$159.3744	$159.37	$159.35	$159.40
7 purchase totals =	$887.82		$951.4805	$951.46	$951.45	$951.50