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	$96.79	10.730%	$107.1756	$107.18	$107.20	$107.20
Purchase #2	$238.83	11.713%	$266.8042	$266.80	$266.80	$266.80
Purchase #3	$62.82	7.847%	$67.7495	$67.75	$67.75	$67.70
Purchase #4	$100.26	3.246%	$103.5144	$103.51	$103.50	$103.50
Purchase #5	$81.47	11.153%	$90.5563	$90.56	$90.55	$90.60
Purchase #6	$106.45	3.270%	$109.9309	$109.93	$109.95	$109.90
Purchase #7	$151.33	8.409%	$164.0553	$164.06	$164.05	$164.10
7 purchase totals =	$837.95		$909.7862	$909.79	$909.80	$909.80