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	$180.88	5.368%	$190.5896	$190.59	$190.60	$190.60
Purchase #2	$10.52	7.631%	$11.3228	$11.32	$11.30	$11.30
Purchase #3	$49.31	11.541%	$55.0009	$55.00	$55.00	$55.00
Purchase #4	$30.25	4.395%	$31.5795	$31.58	$31.60	$31.60
Purchase #5	$83.75	10.337%	$92.4072	$92.41	$92.40	$92.40
Purchase #6	$57.57	11.142%	$63.9844	$63.98	$64.00	$64.00
Purchase #7	$98.54	12.861%	$111.2132	$111.21	$111.20	$111.20
7 purchase totals =	$510.82		$556.0976	$556.09	$556.10	$556.10