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	$64.29	9.671%	$70.5075	$70.51	$70.50	$70.50
Purchase #2	$240.51	7.218%	$257.87	$257.87	$257.85	$257.90
Purchase #3	$167.64	12.244%	$188.1658	$188.17	$188.15	$188.20
Purchase #4	$85.31	5.792%	$90.2512	$90.25	$90.25	$90.30
Purchase #5	$231.54	11.367%	$257.8592	$257.86	$257.85	$257.90
Purchase #6	$227.90	9.234%	$248.9443	$248.94	$248.95	$248.90
Purchase #7	$232.52	11.334%	$258.8738	$258.87	$258.85	$258.90
7 purchase totals =	$1,249.71		$1,372.4718	$1,372.47	$1,372.40	$1,372.60