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	$123.45	12.671%	$139.0923	$139.09	$139.10	$139.10
Purchase #2	$132.62	6.341%	$141.0294	$141.03	$141.05	$141.00
Purchase #3	$200.96	4.387%	$209.7761	$209.78	$209.80	$209.80
Purchase #4	$101.95	4.802%	$106.8456	$106.85	$106.85	$106.80
Purchase #5	$70.83	12.445%	$79.6448	$79.64	$79.65	$79.60
Purchase #6	$110.92	11.676%	$123.871	$123.87	$123.85	$123.90
Purchase #7	$56.60	4.167%	$58.9585	$58.96	$58.95	$59.00
7 purchase totals =	$797.33		$859.2177	$859.22	$859.25	$859.20