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	$56.59	13.283%	$64.1068	$64.11	$64.10	$64.10
Purchase #2	$157.43	12.113%	$176.4995	$176.50	$176.50	$176.50
Purchase #3	$89.58	7.788%	$96.5565	$96.56	$96.55	$96.60
Purchase #4	$127.38	7.252%	$136.6176	$136.62	$136.60	$136.60
Purchase #5	$112.79	5.412%	$118.8942	$118.89	$118.90	$118.90
Purchase #6	$55.47	10.233%	$61.1462	$61.15	$61.15	$61.10
Purchase #7	$10.32	7.794%	$11.1243	$11.12	$11.10	$11.10
7 purchase totals =	$609.56		$664.9451	$664.95	$664.90	$664.90