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	$98.90	13.378%	$112.1308	$112.13	$112.15	$112.10
Purchase #2	$146.71	4.867%	$153.8504	$153.85	$153.85	$153.90
Purchase #3	$143.59	4.688%	$150.3215	$150.32	$150.30	$150.30
Purchase #4	$38.56	8.807%	$41.956	$41.96	$41.95	$42.00
Purchase #5	$147.53	8.143%	$159.5434	$159.54	$159.55	$159.50
Purchase #6	$82.63	3.648%	$85.6443	$85.64	$85.65	$85.60
Purchase #7	$117.77	9.117%	$128.5071	$128.51	$128.50	$128.50
7 purchase totals =	$775.69		$831.9535	$831.95	$831.95	$831.90