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	$72.90	8.788%	$79.3065	$79.31	$79.30	$79.30
Purchase #2	$39.55	7.736%	$42.6096	$42.61	$42.60	$42.60
Purchase #3	$62.79	10.746%	$69.5374	$69.54	$69.55	$69.50
Purchase #4	$105.96	13.765%	$120.5454	$120.55	$120.55	$120.50
Purchase #5	$12.66	12.169%	$14.2006	$14.20	$14.20	$14.20
Purchase #6	$61.37	7.569%	$66.0151	$66.02	$66.00	$66.00
Purchase #7	$38.89	7.609%	$41.8491	$41.85	$41.85	$41.80
7 purchase totals =	$394.12		$434.0637	$434.08	$434.05	$433.90