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	$248.34	3.381%	$256.7364	$256.74	$256.75	$256.70
Purchase #2	$115.69	4.702%	$121.1297	$121.13	$121.15	$121.10
Purchase #3	$81.99	10.765%	$90.8162	$90.82	$90.80	$90.80
Purchase #4	$247.28	10.181%	$272.4556	$272.46	$272.45	$272.50
Purchase #5	$28.76	8.211%	$31.1215	$31.12	$31.10	$31.10
Purchase #6	$49.78	7.736%	$53.631	$53.63	$53.65	$53.60
Purchase #7	$59.46	4.280%	$62.0049	$62.00	$62.00	$62.00
7 purchase totals =	$831.30		$887.8953	$887.90	$887.90	$887.80