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	$176.39	9.505%	$193.1559	$193.16	$193.15	$193.20
Purchase #2	$82.51	10.213%	$90.9367	$90.94	$90.95	$90.90
Purchase #3	$125.42	4.659%	$131.2633	$131.26	$131.25	$131.30
Purchase #4	$144.52	6.300%	$153.6248	$153.62	$153.60	$153.60
Purchase #5	$76.43	7.232%	$81.9574	$81.96	$81.95	$82.00
Purchase #6	$202.75	11.124%	$225.3039	$225.30	$225.30	$225.30
Purchase #7	$38.57	7.817%	$41.585	$41.59	$41.60	$41.60
7 purchase totals =	$846.59		$917.8270	$917.83	$917.80	$917.90