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	$173.57	4.820%	$181.9361	$181.94	$181.95	$181.90
Purchase #2	$246.46	7.150%	$264.0819	$264.08	$264.10	$264.10
Purchase #3	$52.56	9.548%	$57.5784	$57.58	$57.60	$57.60
Purchase #4	$52.63	3.534%	$54.4899	$54.49	$54.50	$54.50
Purchase #5	$81.71	9.554%	$89.5166	$89.52	$89.50	$89.50
Purchase #6	$180.44	7.656%	$194.2545	$194.25	$194.25	$194.30
Purchase #7	$19.32	8.789%	$21.018	$21.02	$21.00	$21.00
7 purchase totals =	$806.69		$862.8754	$862.88	$862.90	$862.90