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	$103.86	5.447%	$109.5173	$109.52	$109.50	$109.50
Purchase #2	$92.76	13.664%	$105.4347	$105.43	$105.45	$105.40
Purchase #3	$88.74	9.693%	$97.3416	$97.34	$97.35	$97.30
Purchase #4	$216.42	8.433%	$234.6707	$234.67	$234.65	$234.70
Purchase #5	$110.44	10.786%	$122.3521	$122.35	$122.35	$122.40
Purchase #6	$38.94	10.588%	$43.063	$43.06	$43.05	$43.10
Purchase #7	$147.78	5.641%	$156.1163	$156.12	$156.10	$156.10
7 purchase totals =	$798.94		$868.4957	$868.49	$868.45	$868.50