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	$211.46	11.699%	$236.1987	$236.20	$236.20	$236.20
Purchase #2	$23.97	12.632%	$26.9979	$27.00	$27.00	$27.00
Purchase #3	$86.49	4.768%	$90.6138	$90.61	$90.60	$90.60
Purchase #4	$166.80	8.267%	$180.5894	$180.59	$180.60	$180.60
Purchase #5	$180.42	3.724%	$187.1388	$187.14	$187.15	$187.10
Purchase #6	$59.25	3.602%	$61.3842	$61.38	$61.40	$61.40
Purchase #7	$115.68	13.229%	$130.9833	$130.98	$131.00	$131.00
7 purchase totals =	$844.07		$913.9061	$913.90	$913.95	$913.90