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	$70.91	11.168%	$78.8292	$78.83	$78.85	$78.80
Purchase #2	$55.94	9.868%	$61.4602	$61.46	$61.45	$61.50
Purchase #3	$180.92	7.552%	$194.5831	$194.58	$194.60	$194.60
Purchase #4	$225.74	5.690%	$238.5846	$238.58	$238.60	$238.60
Purchase #5	$240.49	7.401%	$258.2887	$258.29	$258.30	$258.30
Purchase #6	$250.99	10.447%	$277.2109	$277.21	$277.20	$277.20
Purchase #7	$225.68	12.810%	$254.5896	$254.59	$254.60	$254.60
7 purchase totals =	$1,250.67		$1,363.5463	$1,363.54	$1,363.60	$1,363.60