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	$220.36	13.591%	$250.3091	$250.31	$250.30	$250.30
Purchase #2	$171.64	8.715%	$186.5984	$186.60	$186.60	$186.60
Purchase #3	$100.36	12.490%	$112.895	$112.90	$112.90	$112.90
Purchase #4	$83.84	3.286%	$86.595	$86.60	$86.60	$86.60
Purchase #5	$166.53	13.737%	$189.4062	$189.41	$189.40	$189.40
Purchase #6	$113.73	9.405%	$124.4263	$124.43	$124.45	$124.40
Purchase #7	$234.93	4.640%	$245.8308	$245.83	$245.85	$245.80
7 purchase totals =	$1,091.39		$1,196.0608	$1,196.08	$1,196.10	$1,196.00