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	$132.36	8.546%	$143.6715	$143.67	$143.65	$143.70
Purchase #2	$50.43	13.684%	$57.3308	$57.33	$57.35	$57.30
Purchase #3	$231.54	10.729%	$256.3819	$256.38	$256.40	$256.40
Purchase #4	$136.32	9.539%	$149.3236	$149.32	$149.30	$149.30
Purchase #5	$146.64	10.602%	$162.1868	$162.19	$162.20	$162.20
Purchase #6	$90.71	11.150%	$100.8242	$100.82	$100.80	$100.80
Purchase #7	$203.32	3.676%	$210.794	$210.79	$210.80	$210.80
7 purchase totals =	$991.32		$1,080.5128	$1,080.50	$1,080.50	$1,080.50