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	$111.47	8.747%	$121.2203	$121.22	$121.20	$121.20
Purchase #2	$28.48	12.277%	$31.9765	$31.98	$32.00	$32.00
Purchase #3	$103.52	13.628%	$117.6277	$117.63	$117.65	$117.60
Purchase #4	$146.86	11.686%	$164.0221	$164.02	$164.00	$164.00
Purchase #5	$51.75	4.542%	$54.1005	$54.10	$54.10	$54.10
Purchase #6	$190.87	9.137%	$208.3098	$208.31	$208.30	$208.30
Purchase #7	$86.46	3.588%	$89.5622	$89.56	$89.55	$89.60
7 purchase totals =	$719.41		$786.8191	$786.82	$786.80	$786.80