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	$103.51	7.853%	$111.6386	$111.64	$111.65	$111.60
Purchase #2	$74.53	12.569%	$83.8977	$83.90	$83.90	$83.90
Purchase #3	$20.90	12.771%	$23.5691	$23.57	$23.55	$23.60
Purchase #4	$107.65	8.695%	$117.0102	$117.01	$117.00	$117.00
Purchase #5	$147.69	9.234%	$161.3277	$161.33	$161.35	$161.30
Purchase #6	$106.64	4.641%	$111.5892	$111.59	$111.60	$111.60
Purchase #7	$238.77	4.602%	$249.7582	$249.76	$249.75	$249.80
7 purchase totals =	$799.69		$858.7907	$858.80	$858.80	$858.80