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	$34.56	12.164%	$38.7639	$38.76	$38.75	$38.80
Purchase #2	$80.79	10.868%	$89.5703	$89.57	$89.55	$89.60
Purchase #3	$219.85	9.778%	$241.3469	$241.35	$241.35	$241.30
Purchase #4	$41.51	11.569%	$46.3123	$46.31	$46.30	$46.30
Purchase #5	$175.54	6.778%	$187.4381	$187.44	$187.45	$187.40
Purchase #6	$187.52	12.436%	$210.84	$210.84	$210.85	$210.80
Purchase #7	$205.86	9.610%	$225.6431	$225.64	$225.65	$225.60
7 purchase totals =	$945.63		$1,039.9146	$1,039.91	$1,039.90	$1,039.80