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	$12.64	4.379%	$13.1935	$13.19	$13.20	$13.20
Purchase #2	$108.51	7.647%	$116.8078	$116.81	$116.80	$116.80
Purchase #3	$112.98	12.432%	$127.0257	$127.03	$127.05	$127.00
Purchase #4	$101.69	7.407%	$109.2222	$109.22	$109.20	$109.20
Purchase #5	$162.89	3.374%	$168.3859	$168.39	$168.40	$168.40
Purchase #6	$131.62	10.849%	$145.8995	$145.90	$145.90	$145.90
Purchase #7	$69.49	6.141%	$73.7574	$73.76	$73.75	$73.80
7 purchase totals =	$699.82		$754.2920	$754.30	$754.30	$754.30