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	$238.31	10.570%	$263.4994	$263.50	$263.50	$263.50
Purchase #2	$85.60	9.535%	$93.762	$93.76	$93.75	$93.80
Purchase #3	$73.50	12.655%	$82.8014	$82.80	$82.80	$82.80
Purchase #4	$214.59	8.428%	$232.6756	$232.68	$232.70	$232.70
Purchase #5	$144.28	10.105%	$158.8595	$158.86	$158.85	$158.90
Purchase #6	$17.79	4.866%	$18.6557	$18.66	$18.65	$18.70
Purchase #7	$240.79	13.333%	$272.8945	$272.89	$272.90	$272.90
7 purchase totals =	$1,014.86		$1,123.1481	$1,123.15	$1,123.15	$1,123.30