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	$156.97	10.106%	$172.8334	$172.83	$172.85	$172.80
Purchase #2	$80.25	11.418%	$89.4129	$89.41	$89.40	$89.40
Purchase #3	$8.43	4.306%	$8.793	$8.79	$8.80	$8.80
Purchase #4	$199.93	5.215%	$210.3563	$210.36	$210.35	$210.40
Purchase #5	$52.79	7.638%	$56.8221	$56.82	$56.80	$56.80
Purchase #6	$79.51	11.121%	$88.3523	$88.35	$88.35	$88.40
Purchase #7	$138.59	4.338%	$144.602	$144.60	$144.60	$144.60
7 purchase totals =	$716.47		$771.1720	$771.16	$771.15	$771.20