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	$81.69	4.126%	$85.0605	$85.06	$85.05	$85.10
Purchase #2	$127.34	3.341%	$131.5944	$131.59	$131.60	$131.60
Purchase #3	$206.56	9.599%	$226.3877	$226.39	$226.40	$226.40
Purchase #4	$110.92	4.866%	$116.3174	$116.32	$116.30	$116.30
Purchase #5	$84.63	13.816%	$96.3225	$96.32	$96.30	$96.30
Purchase #6	$101.80	9.530%	$111.5015	$111.50	$111.50	$111.50
Purchase #7	$216.72	7.405%	$232.7681	$232.77	$232.75	$232.80
7 purchase totals =	$929.66		$999.9521	$999.95	$999.90	$1,000.00