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	$209.80	11.841%	$234.6424	$234.64	$234.65	$234.60
Purchase #2	$145.71	5.838%	$154.2165	$154.22	$154.20	$154.20
Purchase #3	$221.98	8.267%	$240.3311	$240.33	$240.35	$240.30
Purchase #4	$126.78	11.660%	$141.5625	$141.56	$141.55	$141.60
Purchase #5	$103.75	10.523%	$114.6676	$114.67	$114.65	$114.70
Purchase #6	$73.25	6.515%	$78.0222	$78.02	$78.00	$78.00
Purchase #7	$116.48	9.175%	$127.167	$127.17	$127.15	$127.20
7 purchase totals =	$997.75		$1,090.6093	$1,090.61	$1,090.55	$1,090.60