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	$75.41	4.219%	$78.5915	$78.59	$78.60	$78.60
Purchase #2	$42.97	4.521%	$44.9127	$44.91	$44.90	$44.90
Purchase #3	$145.52	13.499%	$165.1637	$165.16	$165.15	$165.20
Purchase #4	$87.83	13.426%	$99.6221	$99.62	$99.60	$99.60
Purchase #5	$76.37	12.437%	$85.8681	$85.87	$85.85	$85.90
Purchase #6	$230.49	7.120%	$246.9009	$246.90	$246.90	$246.90
Purchase #7	$59.43	9.508%	$65.0806	$65.08	$65.10	$65.10
7 purchase totals =	$718.02		$786.1396	$786.13	$786.10	$786.20