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	$115.39	11.350%	$128.4868	$128.49	$128.50	$128.50
Purchase #2	$36.49	11.518%	$40.6929	$40.69	$40.70	$40.70
Purchase #3	$143.83	11.464%	$160.3187	$160.32	$160.30	$160.30
Purchase #4	$210.43	4.759%	$220.4444	$220.44	$220.45	$220.40
Purchase #5	$244.35	11.507%	$272.4674	$272.47	$272.45	$272.50
Purchase #6	$162.98	11.196%	$181.2272	$181.23	$181.25	$181.20
Purchase #7	$128.50	7.304%	$137.8856	$137.89	$137.90	$137.90
7 purchase totals =	$1,041.97		$1,141.5230	$1,141.53	$1,141.55	$1,141.50