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	$51.34	5.870%	$54.3537	$54.35	$54.35	$54.40
Purchase #2	$222.29	5.844%	$235.2806	$235.28	$235.30	$235.30
Purchase #3	$72.93	8.661%	$79.2465	$79.25	$79.25	$79.20
Purchase #4	$192.71	6.732%	$205.6832	$205.68	$205.70	$205.70
Purchase #5	$245.77	7.686%	$264.6599	$264.66	$264.65	$264.70
Purchase #6	$80.51	6.332%	$85.6079	$85.61	$85.60	$85.60
Purchase #7	$154.92	6.242%	$164.5901	$164.59	$164.60	$164.60
7 purchase totals =	$1,020.47		$1,089.4219	$1,089.42	$1,089.45	$1,089.50