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	$29.50	8.119%	$31.8951	$31.90	$31.90	$31.90
Purchase #2	$101.49	7.699%	$109.3037	$109.30	$109.30	$109.30
Purchase #3	$129.27	9.141%	$141.0866	$141.09	$141.10	$141.10
Purchase #4	$250.39	3.616%	$259.4441	$259.44	$259.45	$259.40
Purchase #5	$248.56	4.159%	$258.8976	$258.90	$258.90	$258.90
Purchase #6	$6.45	6.657%	$6.8794	$6.88	$6.90	$6.90
Purchase #7	$181.42	9.193%	$198.0979	$198.10	$198.10	$198.10
7 purchase totals =	$947.08		$1,005.6044	$1,005.61	$1,005.65	$1,005.60