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	$160.35	11.190%	$178.2932	$178.29	$178.30	$178.30
Purchase #2	$131.78	12.617%	$148.4067	$148.41	$148.40	$148.40
Purchase #3	$7.55	9.532%	$8.2697	$8.27	$8.25	$8.30
Purchase #4	$55.59	12.423%	$62.4959	$62.50	$62.50	$62.50
Purchase #5	$105.98	4.370%	$110.6113	$110.61	$110.60	$110.60
Purchase #6	$210.29	8.222%	$227.58	$227.58	$227.60	$227.60
Purchase #7	$38.72	8.803%	$42.1285	$42.13	$42.15	$42.10
7 purchase totals =	$710.26		$777.7853	$777.79	$777.80	$777.80