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	$249.29	9.671%	$273.3988	$273.40	$273.40	$273.40
Purchase #2	$169.35	6.406%	$180.1986	$180.20	$180.20	$180.20
Purchase #3	$145.76	6.232%	$154.8438	$154.84	$154.85	$154.80
Purchase #4	$86.52	4.645%	$90.5389	$90.54	$90.55	$90.50
Purchase #5	$97.25	3.493%	$100.6469	$100.65	$100.65	$100.60
Purchase #6	$29.70	6.247%	$31.5554	$31.56	$31.55	$31.60
Purchase #7	$101.78	9.521%	$111.4705	$111.47	$111.45	$111.50
7 purchase totals =	$879.65		$942.6529	$942.66	$942.65	$942.60