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	$125.44	9.180%	$136.9554	$136.96	$136.95	$137.00
Purchase #2	$248.39	13.704%	$282.4294	$282.43	$282.45	$282.40
Purchase #3	$102.71	8.772%	$111.7197	$111.72	$111.70	$111.70
Purchase #4	$203.54	3.511%	$210.6863	$210.69	$210.70	$210.70
Purchase #5	$22.85	7.761%	$24.6234	$24.62	$24.60	$24.60
Purchase #6	$99.90	11.516%	$111.4045	$111.40	$111.40	$111.40
Purchase #7	$136.63	12.365%	$153.5243	$153.52	$153.50	$153.50
7 purchase totals =	$939.46		$1,031.3430	$1,031.34	$1,031.30	$1,031.30