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	$212.86	9.517%	$233.1179	$233.12	$233.10	$233.10
Purchase #2	$156.58	6.796%	$167.2212	$167.22	$167.20	$167.20
Purchase #3	$213.82	10.182%	$235.5912	$235.59	$235.60	$235.60
Purchase #4	$238.76	10.115%	$262.9106	$262.91	$262.90	$262.90
Purchase #5	$61.81	10.512%	$68.3075	$68.31	$68.30	$68.30
Purchase #6	$132.78	4.736%	$139.0685	$139.07	$139.05	$139.10
Purchase #7	$30.86	8.251%	$33.4063	$33.41	$33.40	$33.40
7 purchase totals =	$1,047.47		$1,139.6232	$1,139.63	$1,139.55	$1,139.60