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	$5.86	12.745%	$6.6069	$6.61	$6.60	$6.60
Purchase #2	$43.71	5.846%	$46.2653	$46.27	$46.25	$46.30
Purchase #3	$95.79	4.641%	$100.2356	$100.24	$100.25	$100.20
Purchase #4	$240.86	8.870%	$262.2243	$262.22	$262.20	$262.20
Purchase #5	$126.39	6.564%	$134.6862	$134.69	$134.70	$134.70
Purchase #6	$38.71	9.537%	$42.4018	$42.40	$42.40	$42.40
Purchase #7	$100.54	4.320%	$104.8833	$104.88	$104.90	$104.90
7 purchase totals =	$651.86		$697.3034	$697.31	$697.30	$697.30