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	$46.79	9.822%	$51.3857	$51.39	$51.40	$51.40
Purchase #2	$142.51	11.643%	$159.1024	$159.10	$159.10	$159.10
Purchase #3	$203.50	11.441%	$226.7824	$226.78	$226.80	$226.80
Purchase #4	$98.81	12.589%	$111.2492	$111.25	$111.25	$111.20
Purchase #5	$82.74	4.262%	$86.2664	$86.27	$86.25	$86.30
Purchase #6	$191.60	3.648%	$198.5896	$198.59	$198.60	$198.60
Purchase #7	$215.75	5.357%	$227.3077	$227.31	$227.30	$227.30
7 purchase totals =	$981.70		$1,060.6834	$1,060.69	$1,060.70	$1,060.70