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	$37.64	8.653%	$40.897	$40.90	$40.90	$40.90
Purchase #2	$230.74	10.343%	$254.6054	$254.61	$254.60	$254.60
Purchase #3	$211.30	7.798%	$227.7772	$227.78	$227.80	$227.80
Purchase #4	$72.41	8.333%	$78.4439	$78.44	$78.45	$78.40
Purchase #5	$164.44	10.577%	$181.8328	$181.83	$181.85	$181.80
Purchase #6	$194.57	4.162%	$202.668	$202.67	$202.65	$202.70
Purchase #7	$94.99	10.314%	$104.7873	$104.79	$104.80	$104.80
7 purchase totals =	$1,006.09		$1,091.0116	$1,091.02	$1,091.05	$1,091.00