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	$100.29	3.360%	$103.6597	$103.66	$103.65	$103.70
Purchase #2	$244.59	6.772%	$261.1536	$261.15	$261.15	$261.20
Purchase #3	$57.52	8.484%	$62.4	$62.40	$62.40	$62.40
Purchase #4	$20.39	3.365%	$21.0761	$21.08	$21.10	$21.10
Purchase #5	$23.29	9.836%	$25.5808	$25.58	$25.60	$25.60
Purchase #6	$246.91	12.395%	$277.5145	$277.51	$277.50	$277.50
Purchase #7	$84.89	6.459%	$90.373	$90.37	$90.35	$90.40
7 purchase totals =	$777.88		$841.7577	$841.75	$841.75	$841.90