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	$101.81	10.402%	$112.4003	$112.40	$112.40	$112.40
Purchase #2	$115.90	13.282%	$131.2938	$131.29	$131.30	$131.30
Purchase #3	$48.33	12.204%	$54.2282	$54.23	$54.25	$54.20
Purchase #4	$236.55	10.271%	$260.8461	$260.85	$260.85	$260.80
Purchase #5	$10.30	8.141%	$11.1385	$11.14	$11.15	$11.10
Purchase #6	$167.93	4.152%	$174.9025	$174.90	$174.90	$174.90
Purchase #7	$93.51	7.292%	$100.3287	$100.33	$100.35	$100.30
7 purchase totals =	$774.33		$845.1381	$845.14	$845.20	$845.00