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	$77.58	6.830%	$82.8787	$82.88	$82.90	$82.90
Purchase #2	$91.39	11.693%	$102.0762	$102.08	$102.10	$102.10
Purchase #3	$115.58	10.822%	$128.0881	$128.09	$128.10	$128.10
Purchase #4	$210.87	10.613%	$233.2496	$233.25	$233.25	$233.20
Purchase #5	$89.89	3.846%	$93.3472	$93.35	$93.35	$93.30
Purchase #6	$77.83	3.868%	$80.8405	$80.84	$80.85	$80.80
Purchase #7	$249.58	3.526%	$258.3802	$258.38	$258.40	$258.40
7 purchase totals =	$912.72		$978.8605	$978.87	$978.95	$978.80