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	$133.57	7.359%	$143.3994	$143.40	$143.40	$143.40
Purchase #2	$179.78	9.329%	$196.5517	$196.55	$196.55	$196.60
Purchase #3	$230.59	8.746%	$250.7574	$250.76	$250.75	$250.80
Purchase #4	$186.95	6.479%	$199.0625	$199.06	$199.05	$199.10
Purchase #5	$30.60	3.805%	$31.7643	$31.76	$31.75	$31.80
Purchase #6	$19.54	8.364%	$21.1743	$21.17	$21.15	$21.20
Purchase #7	$34.39	10.669%	$38.0591	$38.06	$38.05	$38.10
7 purchase totals =	$815.42		$880.7687	$880.76	$880.70	$881.00