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	$101.98	5.416%	$107.5032	$107.50	$107.50	$107.50
Purchase #2	$122.28	4.493%	$127.774	$127.77	$127.75	$127.80
Purchase #3	$7.63	12.138%	$8.5561	$8.56	$8.55	$8.60
Purchase #4	$27.34	11.704%	$30.5399	$30.54	$30.55	$30.50
Purchase #5	$43.77	4.156%	$45.5891	$45.59	$45.60	$45.60
Purchase #6	$96.63	8.624%	$104.9634	$104.96	$104.95	$105.00
Purchase #7	$57.54	4.162%	$59.9348	$59.93	$59.95	$59.90
7 purchase totals =	$457.17		$484.8605	$484.85	$484.85	$484.90