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	$40.90	11.613%	$45.6497	$45.65	$45.65	$45.60
Purchase #2	$98.91	13.746%	$112.5062	$112.51	$112.50	$112.50
Purchase #3	$72.98	7.280%	$78.2929	$78.29	$78.30	$78.30
Purchase #4	$202.44	4.661%	$211.8757	$211.88	$211.90	$211.90
Purchase #5	$34.55	3.636%	$35.8062	$35.81	$35.80	$35.80
Purchase #6	$100.56	8.391%	$108.998	$109.00	$109.00	$109.00
Purchase #7	$64.60	10.717%	$71.5232	$71.52	$71.50	$71.50
7 purchase totals =	$614.94		$664.6519	$664.66	$664.65	$664.60