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	$67.96	4.204%	$70.817	$70.82	$70.80	$70.80
Purchase #2	$59.86	12.684%	$67.4526	$67.45	$67.45	$67.50
Purchase #3	$242.46	5.845%	$256.6318	$256.63	$256.65	$256.60
Purchase #4	$80.72	12.246%	$90.605	$90.61	$90.60	$90.60
Purchase #5	$80.61	12.663%	$90.8176	$90.82	$90.80	$90.80
Purchase #6	$235.74	4.300%	$245.8768	$245.88	$245.90	$245.90
Purchase #7	$10.70	12.211%	$12.0066	$12.01	$12.00	$12.00
7 purchase totals =	$778.05		$834.2074	$834.22	$834.20	$834.20