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	$87.41	10.500%	$96.5881	$96.59	$96.60	$96.60
Purchase #2	$112.40	13.542%	$127.6212	$127.62	$127.60	$127.60
Purchase #3	$34.53	11.504%	$38.5023	$38.50	$38.50	$38.50
Purchase #4	$137.58	10.300%	$151.7507	$151.75	$151.75	$151.80
Purchase #5	$107.44	6.625%	$114.5579	$114.56	$114.55	$114.60
Purchase #6	$82.80	6.169%	$87.9079	$87.91	$87.90	$87.90
Purchase #7	$47.80	10.740%	$52.9337	$52.93	$52.95	$52.90
7 purchase totals =	$609.96		$669.8618	$669.86	$669.85	$669.90