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	$249.88	3.425%	$258.4384	$258.44	$258.45	$258.40
Purchase #2	$181.53	5.757%	$191.9807	$191.98	$192.00	$192.00
Purchase #3	$116.82	9.218%	$127.5885	$127.59	$127.60	$127.60
Purchase #4	$129.73	8.775%	$141.1138	$141.11	$141.10	$141.10
Purchase #5	$51.43	10.353%	$56.7545	$56.75	$56.75	$56.80
Purchase #6	$94.64	9.403%	$103.539	$103.54	$103.55	$103.50
Purchase #7	$116.28	3.285%	$120.0998	$120.10	$120.10	$120.10
7 purchase totals =	$940.31		$999.5147	$999.51	$999.55	$999.50