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	$89.27	13.484%	$101.3072	$101.31	$101.30	$101.30
Purchase #2	$236.42	13.632%	$268.6488	$268.65	$268.65	$268.60
Purchase #3	$109.64	6.364%	$116.6175	$116.62	$116.60	$116.60
Purchase #4	$234.45	5.114%	$246.4398	$246.44	$246.45	$246.40
Purchase #5	$114.69	12.286%	$128.7808	$128.78	$128.80	$128.80
Purchase #6	$95.91	8.854%	$104.4019	$104.40	$104.40	$104.40
Purchase #7	$82.97	9.293%	$90.6804	$90.68	$90.70	$90.70
7 purchase totals =	$963.35		$1,056.8764	$1,056.88	$1,056.90	$1,056.80