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	$5.34	8.286%	$5.7825	$5.78	$5.80	$5.80
Purchase #2	$153.28	5.724%	$162.0537	$162.05	$162.05	$162.10
Purchase #3	$203.41	6.340%	$216.3062	$216.31	$216.30	$216.30
Purchase #4	$100.34	5.232%	$105.5898	$105.59	$105.60	$105.60
Purchase #5	$29.56	6.556%	$31.498	$31.50	$31.50	$31.50
Purchase #6	$247.40	7.286%	$265.4256	$265.43	$265.45	$265.40
Purchase #7	$86.98	13.223%	$98.4814	$98.48	$98.50	$98.50
7 purchase totals =	$826.31		$885.1372	$885.14	$885.20	$885.20