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	$89.37	11.650%	$99.7816	$99.78	$99.80	$99.80
Purchase #2	$174.78	7.483%	$187.8588	$187.86	$187.85	$187.90
Purchase #3	$176.90	5.229%	$186.1501	$186.15	$186.15	$186.20
Purchase #4	$17.96	5.508%	$18.9492	$18.95	$18.95	$18.90
Purchase #5	$237.81	9.363%	$260.0762	$260.08	$260.10	$260.10
Purchase #6	$56.83	10.137%	$62.5909	$62.59	$62.60	$62.60
Purchase #7	$213.80	8.410%	$231.7806	$231.78	$231.80	$231.80
7 purchase totals =	$967.45		$1,047.1874	$1,047.19	$1,047.25	$1,047.30