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	$128.91	11.118%	$143.2422	$143.24	$143.25	$143.20
Purchase #2	$116.45	9.760%	$127.8155	$127.82	$127.80	$127.80
Purchase #3	$65.69	7.240%	$70.446	$70.45	$70.45	$70.40
Purchase #4	$145.62	7.193%	$156.0944	$156.09	$156.10	$156.10
Purchase #5	$30.79	9.288%	$33.6498	$33.65	$33.65	$33.60
Purchase #6	$205.92	13.569%	$233.8613	$233.86	$233.85	$233.90
Purchase #7	$196.90	5.411%	$207.5543	$207.55	$207.55	$207.60
7 purchase totals =	$890.28		$972.6635	$972.66	$972.65	$972.60