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	$159.56	10.838%	$176.8531	$176.85	$176.85	$176.90
Purchase #2	$107.32	9.279%	$117.2782	$117.28	$117.30	$117.30
Purchase #3	$220.41	5.503%	$232.5392	$232.54	$232.55	$232.50
Purchase #4	$104.58	7.142%	$112.0491	$112.05	$112.05	$112.00
Purchase #5	$131.95	8.593%	$143.2885	$143.29	$143.30	$143.30
Purchase #6	$71.27	10.269%	$78.5887	$78.59	$78.60	$78.60
Purchase #7	$117.47	8.645%	$127.6253	$127.63	$127.65	$127.60
7 purchase totals =	$912.56		$988.2221	$988.23	$988.30	$988.20