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	$221.39	5.728%	$234.0712	$234.07	$234.05	$234.10
Purchase #2	$135.83	12.178%	$152.3714	$152.37	$152.35	$152.40
Purchase #3	$34.76	7.760%	$37.4574	$37.46	$37.45	$37.50
Purchase #4	$66.85	10.385%	$73.7924	$73.79	$73.80	$73.80
Purchase #5	$241.47	4.196%	$251.6021	$251.60	$251.60	$251.60
Purchase #6	$118.95	12.214%	$133.4786	$133.48	$133.50	$133.50
Purchase #7	$209.77	3.621%	$217.3658	$217.37	$217.35	$217.40
7 purchase totals =	$1,029.02		$1,100.1389	$1,100.14	$1,100.10	$1,100.30