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	$155.40	4.408%	$162.25	$162.25	$162.25	$162.30
Purchase #2	$158.51	13.468%	$179.8581	$179.86	$179.85	$179.90
Purchase #3	$89.77	5.418%	$94.6337	$94.63	$94.65	$94.60
Purchase #4	$104.80	8.170%	$113.3622	$113.36	$113.35	$113.40
Purchase #5	$117.60	7.269%	$126.1483	$126.15	$126.15	$126.10
Purchase #6	$12.77	8.521%	$13.8581	$13.86	$13.85	$13.90
Purchase #7	$178.91	11.738%	$199.9105	$199.91	$199.90	$199.90
7 purchase totals =	$817.76		$890.0209	$890.02	$890.00	$890.10