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	$52.68	5.323%	$55.4842	$55.48	$55.50	$55.50
Purchase #2	$196.75	3.729%	$204.0868	$204.09	$204.10	$204.10
Purchase #3	$86.88	4.568%	$90.8487	$90.85	$90.85	$90.80
Purchase #4	$229.35	10.562%	$253.5739	$253.57	$253.55	$253.60
Purchase #5	$107.98	7.262%	$115.8215	$115.82	$115.80	$115.80
Purchase #6	$51.56	3.808%	$53.5234	$53.52	$53.50	$53.50
Purchase #7	$136.49	4.429%	$142.5351	$142.54	$142.55	$142.50
7 purchase totals =	$861.69		$915.8736	$915.87	$915.85	$915.80