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	$90.98	9.152%	$99.3065	$99.31	$99.30	$99.30
Purchase #2	$164.25	13.128%	$185.8127	$185.81	$185.80	$185.80
Purchase #3	$204.81	6.771%	$218.6777	$218.68	$218.70	$218.70
Purchase #4	$20.52	3.598%	$21.2583	$21.26	$21.25	$21.30
Purchase #5	$247.47	5.455%	$260.9695	$260.97	$260.95	$261.00
Purchase #6	$73.53	6.448%	$78.2712	$78.27	$78.25	$78.30
Purchase #7	$78.58	4.862%	$82.4006	$82.40	$82.40	$82.40
7 purchase totals =	$880.14		$946.6965	$946.70	$946.65	$946.80