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	$52.42	6.273%	$55.7083	$55.71	$55.70	$55.70
Purchase #2	$18.88	11.843%	$21.116	$21.12	$21.10	$21.10
Purchase #3	$152.33	12.799%	$171.8267	$171.83	$171.85	$171.80
Purchase #4	$63.85	5.324%	$67.2494	$67.25	$67.25	$67.20
Purchase #5	$220.41	9.398%	$241.1241	$241.12	$241.10	$241.10
Purchase #6	$38.37	10.838%	$42.5285	$42.53	$42.55	$42.50
Purchase #7	$23.61	12.583%	$26.5808	$26.58	$26.60	$26.60
7 purchase totals =	$569.87		$626.1338	$626.14	$626.15	$626.00