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	$123.59	3.430%	$127.8291	$127.83	$127.85	$127.80
Purchase #2	$160.38	12.613%	$180.6087	$180.61	$180.60	$180.60
Purchase #3	$202.42	12.402%	$227.5241	$227.52	$227.50	$227.50
Purchase #4	$150.69	10.349%	$166.2849	$166.28	$166.30	$166.30
Purchase #5	$229.59	9.156%	$250.6113	$250.61	$250.60	$250.60
Purchase #6	$79.70	7.414%	$85.609	$85.61	$85.60	$85.60
Purchase #7	$54.97	8.643%	$59.7211	$59.72	$59.70	$59.70
7 purchase totals =	$1,001.34		$1,098.1882	$1,098.18	$1,098.15	$1,098.10