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	$108.70	8.189%	$117.6014	$117.60	$117.60	$117.60
Purchase #2	$31.86	9.222%	$34.7981	$34.80	$34.80	$34.80
Purchase #3	$33.41	6.501%	$35.582	$35.58	$35.60	$35.60
Purchase #4	$78.46	10.111%	$86.3931	$86.39	$86.40	$86.40
Purchase #5	$108.25	10.862%	$120.0081	$120.01	$120.00	$120.00
Purchase #6	$133.86	4.244%	$139.541	$139.54	$139.55	$139.50
Purchase #7	$89.76	4.330%	$93.6466	$93.65	$93.65	$93.60
7 purchase totals =	$584.30		$627.5703	$627.57	$627.60	$627.50