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	$70.76	8.507%	$76.7796	$76.78	$76.80	$76.80
Purchase #2	$161.28	6.411%	$171.6197	$171.62	$171.60	$171.60
Purchase #3	$241.48	13.164%	$273.2684	$273.27	$273.25	$273.30
Purchase #4	$231.66	13.459%	$262.8391	$262.84	$262.85	$262.80
Purchase #5	$171.34	3.675%	$177.6367	$177.64	$177.65	$177.60
Purchase #6	$106.25	5.236%	$111.8133	$111.81	$111.80	$111.80
Purchase #7	$34.26	10.152%	$37.7381	$37.74	$37.75	$37.70
7 purchase totals =	$1,017.03		$1,111.6949	$1,111.70	$1,111.70	$1,111.60