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	$96.31	4.109%	$100.2674	$100.27	$100.25	$100.30
Purchase #2	$192.81	12.472%	$216.8573	$216.86	$216.85	$216.90
Purchase #3	$164.76	3.493%	$170.5151	$170.52	$170.50	$170.50
Purchase #4	$209.45	13.839%	$238.4358	$238.44	$238.45	$238.40
Purchase #5	$170.30	10.418%	$188.0419	$188.04	$188.05	$188.00
Purchase #6	$82.90	5.837%	$87.7389	$87.74	$87.75	$87.70
Purchase #7	$74.54	13.652%	$84.7162	$84.72	$84.70	$84.70
7 purchase totals =	$991.07		$1,086.5726	$1,086.59	$1,086.55	$1,086.50